trifocal

trifocal

[trahy-foh-kuhl, trahy-foh-]
adjective
1.
Optics. having three foci.
2.
(of an eyeglass lens) having three portions, one for near, one for intermediate, and one for far vision.
noun
3.
trifocals, eyeglasses with trifocal lenses.

Origin:
1945–50; tri- + focal

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Based on the Random House Dictionary, © Random House, Inc. 2014.
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Collins
World English Dictionary
trifocal
 
adj
1.  having three focuses
2.  having three focal lengths
 
n
3.  (plural) glasses with trifocal lenses

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