bi-
/baɪ/combining form
1- two; having two表示“二”, “具有两个”：
bicoloured
biathlon.
参见BIN-.
1.1
- occurring twice in every one or once in every two表示“每…两次”, “每两…一次”：
bicentennial.
1.2
- lasting for two表示“持续两…的”：
biennial.
1.3
- doubly; in two ways表示“两倍”, “两方面地”：
biconcave.
1.4
- Chemistry (in names of compounds) containing two atoms or groups of a specified kind【化】［用于化合物名称］表示“联（二）”：
bicarbonate.
1.5
- Botany & Zoology (of division and subdivision) twice over【植, 动】表示“（部或亚门）二回”：
bipinnate.
USAGE
The meaning of bimonthly （and other similar words such as biweekly and biyearly） is ambiguous. Such words can either mean 'occurring or produced twice a month' or 'occurring or produced every two months'. The only way to avoid this ambiguity is to use alternative expressions like every two months and twice a month. Biannual and biennial are also confusing: biannual means 'occurring twice a year' and biennial means 'occurring every two years'.
词源
from Latin, 'doubly, having two'; related to Greek di- 'two'.