Douglas Harper's Etymology Dictionary
Wiktionary
trifocals
n. (context optics English) spectacles with corrective lenses that have three different powers per eye.
Usage examples of "trifocals".
Scott taking off her Chanel suit, her trifocals, her diamond-encrusted designer crucifix, then embracing her beach boy.
With his high power trifocals slid up onto his pink, unsunned brow, the D/Crypt tech busily packed up his equipment cases.
His trifocals, unchanged, were still necessary if he were to see anything clearly, near or far.