Definitions

from the GNU version of the Collaborative International Dictionary of English.

  • noun plural eyeglasses whose lenses have two foci, allowing the wearer to see both far and nearby objects clearly. The lenses are partitioned horizontally, the upper and lower parts having different focal lengths.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun spectacles that have corrective lenses of two different powers; used by people who need both distance and reading glasses

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun eyeglasses having two focal lengths, one for near vision and the other for far vision

Etymologies

from Wiktionary, Creative Commons Attribution/Share-Alike License

From bi- + focal (see focus), coined in 1824 by John Isaac Hawkins, inventor of trifocals. When the concept of bifocals was originally conceived by Benjamin Franklin, he called them double spectacles.

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