Originally: each of a number of minute spines or processes on the abdominal surface of certain subterranean insect pupae, used in locomotion (usually in plural; now rare). Later also: an unpaired accessory sclerite in the genitalia of certain male flies.
Each of a number of tapering processes on the internal surface of the shell of certain articulated brachiopods. Usually in plural.
Early 19th century; earliest use found in William Kirby (1759–1850), entomologist and naturalist. From classical Latin adminiculum prop, support, in scientific Latin also accessory organ of a plant used for support, defence, etc. (G. A. ScopoliFundamenta botanica 20).