I. “+ adjective
Etymology: tri- + focal
1. : having three focal lengths
2. of an eyeglass lens : having one part that corrects for near vision, one for intermediate vision (as at arm's length), and one for distant vision
II. noun
( -s )
1. : a trifocal glass or lens
2. trifocals plural : eyeglasses with trifocal lenses — compare bifocal 2