early 15c., "existence, independence," from Late Latin subsistentia "substance, reality," from Latin subsistens, present participle of subsistere "stand still or firm," from sub "under, up to" (see sub-) + sistere "to assume a standing position," from stare "to stand" (see assist). Properly a loan-translation of Greek hypostasis "subsistence," literally "anything placed under." Meaning "provision of support for animal life" is from 1640s.