Bi-  comb. Form forming nouns, adjectives, and verbs, meaning: 1 division into two (biplane; bisect). 2 a occurring twice in every one or once in every two (bi-weekly). B lasting for two (biennial). 3 chem. Substance having a double proportion of what is indicated by the simple word (bicarbonate). 4 bot. & zool. Having divided parts which are themselves similarly divided (bipinnate). [latin]