Real Dictionary

monthly
A monthly event or publication happens or appears every month.

monthly in American English
done, happening, payable, etc. once a month, or every month
adjective: pertaining to a month, or to each month
adverb: once a month; by the month
noun: a periodical published once a month

monthly in British English
adjective: occurring, done, appearing, payable, etc, once every month
adverb: once a month
noun: a book, periodical, magazine, etc, published once a month