I just read a note from someone who suggested that one writer had "calumnized" another. I responded that calumny is a noun, never a verb. The person responded that this is not necessarily so. Really?

OED2 has calumnize (obs) and calumny as equivalent to calumniate.

Well, I can tell I never took Latin. Calumnize would be my verb of choice; calumniate sounds awkward and wrong to me, but looking at the etymology I can see that it came straight from the Latin.
Like Father Steve (hi, you! ), I think of calumny as a noun, though, as in, "What he said about me was a calumny". But what would be the verb (if there is one) to express the act?
Commit a calumny? Stated a calumny?

The Latin verb is calumniari, to accuse falsely, misrepresent. Perhaps someone knows similarly formed verbs (1st declension, deponent) in Latin that have made their way into English for guidance in forming the proper English verb.

Seems plain awkward to me. I think the fact that the OED calls it obsolete says all that needs to be said!

Faldage sez: "The Latin verb is calumniari."

"Calumniari" is actually fried squid, served, in the Italian fashion, with a red sauce, or in the Greek fashion, with a lovely sauce based on unflavoured yoghurt, garlic, olive oil and lemon juice.

To "calumniaricize" someone is therefor to offer them some deep-fried squid with a nice sauce on the side.

I frequently calumnize when I'm doing spread sheets!