1778, from Modern Latin suffixum, noun use of neuter of Latin suffixus "fastened," past participle of suffigere "fasten, fix on, fasten below," from assimilated form of sub "under, up from under" (see sub-) + figere "to fasten, fix" (from PIE root *dheigw- "to stick, fix"). Related: Suffixal.
in the grammatical sense, 1778, from suffix (n.). Earlier "to put or place under" (c. 1600). Related: Suffixed; suffixing.