*gwelə-, also *gwel-, Proto-Indo-European root meaning "to throw, reach," with extended sense "to pierce."
It forms all or part of: anabolic; arbalest; astrobleme; ball (n.2) "dancing party;" ballad; ballet; ballista; ballistic; ballistics; belemnite; catabolism; devil; diabolical; discobolus; emblem; embolism; hyperbola; hyperbole; kill (v.); metabolism; palaver; parable; parabola; parley; parliament; parlor; parol; parole; problem; quell; quail (v.) "lose heart, shrink, cower;" symbol.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit apa-gurya "swinging," balbaliti "whirls, twirls;" Greek ballein "to throw, to throw so as to hit," also in a looser sense, "to put, place, lay," bole "a throw, beam, ray," belemnon "dart, javelin," belone "needle," ballizein "to dance;" Armenian kelem "I torture;" Old Church Slavonic zali "pain;" Lithuanian galas "end," gėla "agony," gelti "to sting."
"female dancer," especially a ballet-dancer," 1828, from French, fem. of danseur, agent noun from danser (see dance (v.)). The earlier word in English was danceress (Middle English daunceresse, late 14c.).