The situation is the same with “bimonthly,” which can mean “twice a month” and “every two months.”
bimonthly, bī-munth′li, adj. once in two months; also twice a month.
He explained that his pay was six rupees a month paid bimonthly.
For a long time now he has eaten of the white man's lotos—the bimonthly beef-issue.
bimonthly election of the priors of Urbino, with certain powers, and with a salary of fifteen ducats.
Sessions for the trial of grave criminal cases are held monthly, bimonthly, or quarterly, according to circumstances.
Bimensal, bī-mens′al, adj. happening once in two months: bimonthly.