early 15c., "accumulation of morbid matter in the body," from Old French congestion (14c.) and directly from Latin congestionem (nominative congestio) "a heaping up," noun of action from past participle stem of congerere "to bring together, pile up," from assimilated form of com "with, together" (see con-) + gerere "to carry, perform" (see gest). Medical sense "unnatural accumulation of fluid" is from 1630s; meaning "a crowding together of people, traffic, etc." is from 1883.
