bi-
pref 前缀 two; twice 二; 两次: biannual
bicentenary. Cf 参看 di-, tri-. bi-, NOTE ON USAGE 用法
Note that bi- is used with certain expressions of time (eg bimonthly) to mean both `every two' (months) and `twice a' (month) 注意bi-附加在某些表示时间的词语前面（如 bimonthly）, 兼有｀每两＇（月）和（每月）｀两次＇两种含义. There is a distinction between biennial (every two years) and biannual (twice a year). *biennial意为｀每两年＇, biannual意为｀每年两次＇, 这二者的区别则十分清楚.