1610s, "deductive reasoning," from Latin synthesis "collection, set, suit of clothes, composition (of a medication)," from Greek synthesis "composition, a putting together," from syntithenai "put together, combine," from syn- "together" (see syn-) + tithenai "put, place" (see theme). From 1733 as "a combination of parts into a whole." Earlier borrowed in Middle English as sintecis (mid-15c.). Plural syntheses.