"requite, repay, or return in kind," 1610s, from Latin retaliatus, past participle of retaliare "pay back in kind," from re- "back" (see re-) + Latin talio "exaction of payment in kind," from or influenced by talis "suchlike" (see that). Originally of kindness, civility, etc., but by 1630s of injury, ill-treatment, etc. (now the usual sense). Intransitive sense is from 1650s. Related: Retaliated; retaliating.
adjective and noun suffix, "having to do with, characterized by, tending to, place for," from Middle English -orie, from Old North French -ory, -orie (Old French -oir, -oire), from Latin -orius, -oria, -orium.
Latin adjectives in -orius, according to "An Etymological Dictionary of the French Language," tended to "indicate a quality proper to the action accomplished by the agent; as oratorius from orator; laudatorius from laudator. The neuter of these adjectives was early employed as a substantive, and usually denoted the place of residence of the agent or the instrument that he uses; as praetorium from praetor; dormitorium from dormitor; auditorium, dolatorium.
"These newer words, already frequent under the Empire, became exceedingly numerous at a later time, especially in ecclesiastical and scholastic Latin; as purgatorium, refectorium, laboratorium, observatorium, &c." [transl. G.W. Kitchin, Oxford, 1878]
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Harper, D. (n.d.). Etymology of retaliatory. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/retaliatory