Occurring, done, or coming, once in two months; as, bimonthly visits; bimonthly publications.
According to Webster, bi can mean every two months or twice a month. And semi can also lead to misunderstanding. Perhaps it is better to state what you mean by simply stating either "every two months" or "twice each month."
Issue in alternate months; published six times a year
a periodical that is published bimonthly
occurring twice a month; "a semimonthly publication"
occurring every two months; "bimonthly visits"
twice a month; "salaries are paid semimonthly"
every two months; "the bill was payable bimonthly"
Issued in alternate months. Thus, published six times a year. Compare Semimonthly.
Published every other month.
Publication issued every two months.
Bimonthly is a reference to an event that occurs once every two months. An example of a bimonthly event would be the production of some magazines, that have lower subscription numbers or other budgetary or content restrictions, which would total 6 issues per year rather than the more common weekly (once per week), bi-weekly (every two weeks) and monthly (once per month) printings.