Why is the ninth month called September?
1610s, "act of investing with some quality," from Medieval Latin specificationem (nominative specificatio), from Latin species "kind, sort" (see species) + -ficus, unstressed comb. form of facere "to make, do." Meaning "technical particular" is attested from 1833; short form spec first attested 1956.
(spec) A document describing how some system should work.