From WordNet (r) 3.0 (2006) [wn]:
scuba
n 1: a device (trade name Aqua-Lung) that lets divers breathe
under water; scuba is an acronym for self-contained
underwater breathing apparatus [syn: aqualung, {Aqua-
Lung}, scuba]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Self-contained Underwater Breathing Apparatus \Self`-con*tained"
Underwater Breathing Apparatus\, n.
A portable device to allow divers to breathe while under
water, consisting of one or two tanks of compressed air which
are strapped onto the back of the diver, and are connected by
tubing to a mouthpiece through which the diver receives the
air from the tanks at rate adjustable by a valve; -- called
also SCUBA, SCUBA gear, or SCUBA apparatus.
[PJC]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
aqualung \aqualung\ n.
an apparatus containing compressed air or other oxygen-gas
mixture, permitting a person to breathe under water; -- also
called a scuba.
Syn: scuba
[WordNet 1.5 +PJC]