Killology is said to be “the study of the psychological and physiological effects of killing and combat on the human psyche” and the term is said to have been coined by the retired Lt. Col. Dave Grossman (US Army). Perhaps I may be the first person to try to employ the word “killology” in a Buddhist context. I would, however, propose to define “Buddhist Killology” (or perhaps better “Buddhist Cideology,” from French -cide, from Latin cida “cutter, killer”) as a “scholarly study of the Buddhist attitude towards the act of killing.” For the sake of discussing the Buddhist attitude toward killing, one might primarily consider those x-cide words. To be noted is that an x-cide word usually mean one of these four things: (a) “killing x,” where x is an animate or sentient being (e.g. matricide), (b) “killing through or by means of x,” where x is often a tangible entity (e.g. autocide),(c) “a kind of substance that is used to kill x,” where x is often a nuisance-causing and hence unwanted small creature such as bug or vermin (e.g. German Ungetier and Ungeziefer) (e.g. pesticide), or (d) the act of destroying x (literarily or figuratively), where x is usually an inanimate and intangible entity (e.g. chronocide “the killing or wasting of time,” famacide “the killing of another’s reputation, a slander,” liberticide “the destruction of liberties, linguicide “intentionally causing the death of a language,” and libricide “the destruction of books and libraries mainly with a religious or political ideology”). Our main concern in this context would be x-cide in the first sense.
Some random points may be made in this regard. First of all, killing may be defined by Buddhist sources as a physical act of the destruction or cutting (short) of or putting an abrupt end to life or life-faculty (jīvendriya: srog gi dbang po) of a sentient being. Naturally therefore the issue of what is sentient is crucial in Buddhism. Lambert Schmithausen’s study of the issue of sentiency of plants in Buddhism should be presupposed here. According to him and if I remember correctly, Buddhists in the beginning were reticent about the sentiency of plants and that plants were considered borderline cases by them but in course of time, they decided in favor of the in-sentiency of plants. In other words, according to Buddhism, plants may be considered living things but not living or sentient beings. Killing here thus refers to only killing of sentient beings.
Second, killing, being a physical or bodily act or deed in Buddhism, can never be considered categorically or apodictically unwholesome, wholesome, or neutral, although most acts or deeds of killing would be committed through motives tinged by intellectual-emotional defilements (kleśa: nyon mongs pa) such as desire, hatred, greed, jealousy, and so forth, and thus considered unwholesome ethically, morally, spiritually (or ascetically), and karmically (or legally). The most decisive factor is thus the wholesomeness, unwholesomeness, or neutrality of the preceding, accompanying, or concluding volitional impulse or motivation of the main agent of the act of killing. I specify here “main agent” to exclude a “commissioned killer” (who may be mostly considered an instrument of killing). A “commissioned killer” may or may not be an accomplice in the volitionary act of killing. The equivocality or equivocacy of the act of killing in terms of ethical, moral, spiritual (or ascetic), and karmic positivity, negativity, or neutrality, makes the act of killing one of the greatest challenges in Buddhist philosophy. I may have killed a person and claim that I did it out of pure compassion and benevolence. I may have killed a person out of pure hatred and maliciousness. I may have killed someone in the course of a sleep-walking. Can one, who can, and how can one determine the positivity, negativity, or neutrality of the motive behind an act of killing and thus judge accordingly as wholesome, unwholesome, and neutral?
Third, one may classify types of killing in several ways. Killing may be classified based on (a) the kind of species of sentient being killed (e.g. homicide “killing of a human being”), (b) the killer’s family and other relationship with the victim (i.e. matricide and patricide), (c) spiritual or social status (e.g. regicide “the killing of a monarch”), (d) ways of killing (i.e. capital punishment “the judicial killing of a human being for odious crimes” and euthanasia (also mercy killing) “the killing of any being for compassionate reasons i.e. significant injury or disease,” and so on. But perhaps all types of killing maybe subsumed under suicide (i.e. intentional killing oneself) and paracide (i.e. intentional killing of other sentient beings). For suicide, see q.v. Buddhist Suicidology.
Fourth, the gravity of the act of killing and thus also the karmic (or legal) accountability for it would be determined by a number of factors. Some of such factors presupposed in Buddhism seem to be (a) the size of physical size of a sentient being (e.g. it is not the same killing an ant and an elephant), (b) number of sentient beings (e.g. whether one kills one cow or a thousand cows), (c) the frequency (e.g. whether one kills a sentient being once or regularly), (d) the intensity or extensity of preceding, accompanying, and concluding volitional impulse, (e) the degree or extent to which the victim happens to be a guṇakṣetra (yon tan gyi zhing) or puṇyakṣetra (bsod nams kyi zhing), that is, even among human beings it would depend whether the victim is a parent, patient, saint, and the like.
In Buddhism, I doubt that a human being can kill a celestial being (i.e. god) and hence deicide would be, according to Buddhism, an impossibility. Similarly, Buddhocide (i.e. “the killing of the Buddha or a buddha”) would be an impossibility. Nobody can ever kill the Buddha or a buddha! To be noted is that not everyone who is said to possess the Buddha (or Buddhomorphic) Element (buddhadhātu: sangs rgyas kyi khams) can be considered a buddha. Perhaps hagiocide (i.e. killing of a saint), however, is possible insofar as one may be able to kill an arhant or a bodhisattva would get killed. The killing of Tibetan king ’U-dum-btsan may be regarded by Tibetan Buddhists as tyrannicide (i.e. “the killing of a tyrant”), which would be theoretically endorsable. Self-immolation (i.e. suicide by setting oneself on fire, a form of extreme protest), like any other form of suicide or paracide, is subject to equivocality. From a Buddhist point, there would be nothing honorable about the so-called “honor killing” (i.e. the act of killing a family member who has or was perceived to have brought disgrace to the family) would be categorically and apodictically considered reproachable and dishonorable. What about judicial killing? Judicial system is a worldly system and Buddhism (initially and mainly as a discipline of attaining release from the bondage of saṃsāra) would not normally lay down legal systems for the society unless a king or a country happens to follow Buddhist teachings. Some Buddhists may even see a country’s law a kind of jungle’s law and would only hope that people in the jungle would not unjustly send one to the gallows. To change a political or legal system of a country, lay and ordained Buddhist community would have to meddle into and muddle in the dirty waters of politics. One would be free to do so if one can and will but would that be the raison d’être of Buddhist teachings in the first place? What about Euthanasia? Difficult! How can one ensure and be sure that “mercy killing” is indeed merciful and beneficial? Buddhism is bound to view the very intent of genocide (i.e. the systematic extermination of an entire national, racial, religious, or ethnic group) and particularly omnicide (i.e. the act of killing all humans, to create intentional extinction of the human species) heinous. How might Buddhism view human sacrifice (i.e. the killing of a human for religious reasons)? Perhaps it would be viewed as a practice based on completely erroneous views. What about dominicide (i.e. the act of killing one’s (Buddhist) master? It would be usually viewed very negatively. What about episcopicide (i.e. the act of killing a bishop) or vaticide (i.e. the act of killing a prophet)? It may depend on what kind of person that particular bishop or prophet is. If he or she happens to be a person who spreads religion of hate and destruction, a bodhisattva or tāntrika might consider “liberating” him or her. If he or she happens to contribute to compassion, insight, happiness, and peace in the world, episcopicide and vaticide would be a heinous crime.