BI-

comb. form (often bin- before a vowel) forming nouns and adjectives meaning: 1 having two; a thing having two (bilateral; binaural; biplane). 2 a occurring twice in every one or once in every two (bi-weekly). b lasting for two (biennial). 3 doubly; in two ways (biconcave). 4 Chem. a substance having a double proportion of the acid etc. indicated by the simple word (bicarbonate). 5 Bot. & Zool. (of division and subdivision) twice over (bipinnate). [L]