Meaning

noun a periodical that is published every month (or 12 issues per year)

adjective of or occurring or payable every month

adverb occurring once a month

originFrom month + -ly (adjectival suffix), perhaps via Middle English *monethly (attested only adverbially), from Old English mōnaþlīċ (“monthly”), from Proto-West Germanic *mānōþlīk, from Proto-Germanic *mēnōþlīkaz (“monthly”). Cognate with Saterland Frisian moundelk (“monthly”), German monatlich (“monthly”), Danish månedlig (“monthly”), Swedish månatlig (“monthly”), Norwegian Bokmål månedlig…

Etymology from Wiktionary, CC BY-SA 3.0