The definition of bimonthly is happening every two months, or it could be used in place of semimonthly to mean twice a month. 1  An example of bimonthly used as an adjective is the phrase a bimonthly bill which means a bill that comes every two months. An example of bimonthly used as an adjective is the phrase a bimonthly paycheck which means a paycheck that comes two times a month.