DictionaryRoot: bi-
Latin
bi-
two or twice
Forms
- bi-
- bis- — A related fuller Latin form, especially meaning “twice.”
Origin
From an older form related to Latin duo, “two.”
Note
Two parts, two occurrences, and doubling are related but distinct uses of the prefix.
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noun / adjective
bifocal
bye-FOH-kul/ˌbaɪˈfəʊkl/
A lens with two optical powers for near and distant vision, or having this design.
Etymology
The pieces mean “having two foci.” In the selected optical sense, this corresponds to two focusing powers: one for nearby objects and another for distant ones.