■ adjective
1》 happening quickly or promptly.
2》 moving or capable of moving at high speed.
■ adverb literary except in combination ~ly: a ~-acting poison.
■ noun
1》 a fast-flying insectivorous bird with long, slender wings, spending most of its life on the wing. [ Apus apus (Eurasia) and other species, family Apodidae.]
2》 a moth, typically yellow-brown, with fast darting flight. [Family Hepialidae.]
3》 a light adjustable reel for holding a skein of silk or wool.
Derivatives
~ly adverb
~ness noun
Origin
OE, from the Gmc base of OE swīfan 'move in a course, sweep'.