1610s, "act of investing with some quality," from Medieval Latin specificationem (nominative specificatio), noun of action from past participle stem of Late Latin specificare "mention particularly," from Latin specificus, (see specific). With Latin -ficus "making, doing," from combining form of facere "to make, do." Meaning "technical particular" is attested from 1833; short form spec first attested 1956.
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Harper, D. (n.d.). Etymology of spec. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/spec