killable (adj.)

c. 1200, "to strike, hit, beat, knock;" c. 1300, "to deprive of life, put to death;" perhaps from an unrecorded variant of Old English cwellan "to kill, murder, execute," from Proto-Germanic *kwaljanan (source also of Old English cwelan "to die," cwalu "violent death;" Old Saxon quellian "to torture, kill;" Old Norse kvelja "to torment;" Middle Dutch quelen "to vex, tease, torment;" Old High German quellan "to suffer pain," German quälen "to torment, torture"), from PIE root *gwele- "to throw, reach," with extended sense "to pierce." Related: Killed; killing.

The meaning "to nullify or neutralize the qualities of" is attested from 1610s. Of time, from 1728; of engines, from 1886; of lights, from 1934. Kill-devil, colloquial for "rum," especially if new or of bad quality, is from 1630s. Dressed to kill is first attested 1818 in a letter of Keats (compare killing (adj.) in the sense "overpowering, fascinating, attractive").

common termination and word-forming element of English adjectives (typically based on verbs) and generally adding a notion of "capable of; allowed; worthy of; requiring; to be ______ed," sometimes "full of, causing," from French -able and directly from Latin -abilis. It is properly -ble, from Latin -bilis (the vowel being generally from the stem ending of the verb being suffixed), and it represents PIE *-tro-, a suffix used to form nouns of instrument, cognate with the second syllables of English rudder and saddle (n.).

A living element in English, used in new formations from either Latin or native words (readable, bearable) and also with nouns (objectionable, peaceable). Sometimes with an active signification (suitable, capable), sometimes of neutral signification (durable, conformable). It has become very elastic in meaning, as in a reliable witness, a playable foul ball, perishable goods. A 17c. writer has cadaverable "mortal."

To take a single example in detail, no-one but a competent philologist can tell whether reasonable comes from the verb or the noun reason, nor whether its original sense was that can be reasoned out, or that can reason, or that can be reasoned with, or that has reason, or that listens to reason, or that is consistent with reason; the ordinary man knows only that it can now mean any of these, & justifiably bases on these & similar facts a generous view of the termination's capabilities; credible meaning for him worthy of credence, why should not reliable & dependable mean worthy of reliance & dependence? [Fowler]

In Latin, -abilis and -ibilis depended on the inflectional vowel of the verb. Hence the variant form -ible in Old French, Spanish, English. In English, -able tends to be used with native (and other non-Latin) words, -ible with words of obvious Latin origin (but there are exceptions). The Latin suffix is not etymologically connected with able, but it long has been popularly associated with it, and this probably has contributed to its vigor as a living suffix.

1841, from un- (1) "not" + killable.