bi- repr. L. bi- (earlier dui- = Gr. di-, Skr. dvi-) twice, doubly, two-, in L. chiefly in adj. formations on sb. stems, as BICEPS, bicolor of two colours, also with pp. ending, as biformātus of two forms; in a few, e.g. BIFID, the formation is on a vb.-stem. The prefix appears in Eng. first in adoptions from F., as bigam XIII (cf. BIGAMOUS), later from L. words, as biformed XVI (L. biformis), bipartite XVI (L. bipartītus). From XVII the L. analogy was widely extended and the prefix used with any adj. to express that a quality or property is doubled or repeated; in mod. scientific terminology forms in -ate, -ated are most frequently employed.

bi- combining form denoting two; double.