The Collaborative International Dictionary of English v.0.48:
Triple \Tri"ple\, a. [L. triplus; tri- (see Tri-) + -plus, as
in duplus double: cf. F. triple. See Double, and cf.
1. Consisting of three united; multiplied by three;
threefold; as, a triple knot; a triple tie.
By thy triple shape as thou art seen. --Dryden.
2. Three times repeated; treble. See Treble.
3. One of three; third. [Obs.] --Shak.
Triple crown, the crown, or tiara, of the pope. See
Triple-expansion steam engine, a compound steam engine in
which the same steam performs work in three cylinders
Triple measure (Mus.), a measure of tree beats of which
first only is accented.
Triple ratio (Math.), a ratio which is equal to 3.
Triple salt (Chem.), a salt containing three distinct basic
atoms as radicals; thus, microcosmic salt is a triple
Triple star (Astron.), a system of three stars in close
Triple time (Mus.), that time in which each measure is
divided into three equal parts.
Triple valve, in an automatic air brake for railroad cars,
the valve under each car, by means of which the brake is
controlled by a change of pressure in the air pipe leading
from the locomotive.