residual adj.

mid-14c., "the remainder, that which is left after a part is taken," from Old French residu (14c.), from Latin residuum "a remainder, that which is left behind," noun use of neuter of adjective residuus "remaining, left over," from residere "remain behind" (see reside). In law, "what remains of an estate after debts, etc. have been paid," early 15c. The Latin original residuum also sometimes was used in English, especially in reference to the physical matter left after any process.

suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).

suffix forming nouns of action from verbs, mostly from Latin and French, meaning "act of ______ing" (such as survival, referral), Middle English -aille, from French feminine singular -aille, from Latin -alia, neuter plural of adjective suffix -alis, also used in English as a noun suffix. Nativized in English and used with Germanic verbs (as in bestowal, betrothal).