'Triple' is Latin for 'threefold' — from 'tri-' + '-plus' (fold). Part of the simplex/duplex/triplex series.
Consisting of three parts or things; three times as much or as many. As a verb, to make or become three times as large.
From Old French 'triple,' from Latin 'triplus' (threefold), from 'tri-' (three) + the root of '-plus' / '-plex' (fold, layer), related to 'plicāre' (to fold) and the PIE root *pleḱ- (to plait, to fold). Something triple is literally 'three-fold.' Latin formed a systematic series: 'simplex' (one-fold, simple), 'duplex' (two-fold, double), 'triplex' (three-fold, triple), 'multiplex' (many-fold). The PIE
English has two words for 'three times as much': 'triple' (from Latin 'triplus') and 'treble' (from Latin 'tripalium' via Old French 'treble'). In most contexts they are interchangeable, but usage has split by domain: sports prefer 'triple' (triple play, triple jump), while music strongly prefers 'treble' (treble clef). British English uses 'treble' more broadly than American English.