Bimonthly = 1) twice a month 2) once every two months It isn't often used because it does have 2 very different meanings.

They're both correct. "Bi-" is a prefix that comes from Latin meaning "two." Besides "bimonthly," you also have the confusing "biweekly" and "biannually/biennially." Generally with "bimonthly" and "biweekly," we interpret those words as meaning "every two months" and "every two weeks," even though they can be interpreted as "twice a month" and "twice a week." If we mean "twice a month" or "twice a week," we'll often say and write it that way because we know "bimonthly" and "biweekly" can be interpreted either way.

It means both. But apparently in the publishing industry, bimonthly usually means every two months: http://oxforddictionaries.com/words/does-bimonthly-mean-twice-a-month-or-every-two-months

隔月刊 かくげつかん published bimonthly

BIcycle, BIsexual, it means 2, something with 2.