Term for monthly (variation)?

Is there a word for monthly, as in, say, monthly variation. I’m looking for a word in the same sense as quotidian or septadian.

Many thanks.

“Mensual.” The word “menstrual” originally connoted “monthly,” but it has now taken on a more particular meaning, and Webster’s lists its meaning of “monthly” as archaic.

“Quotidian” I know. What is “septadian”?

“Bi-fortnightly.”

“Quadweekian.”

I stand to be corrected, but I take it to mean having a seven day cycle, i.e. weekly.

Excellent. The word doesn’t appear in my unabridged dictionary, but I did find several instances online, all in medical journals (as in “septadian rhythm”).

I’ve come back to this thread three times now. I have to ask: what is the same sense? I mean, why isn’t “monthly” just the word you’re looking for?