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.