ahd gives a good definition but no origins.
Dictionary.com artfully offers: [Origin: 1585–95; woman + -ize]
I can’t imagine that womanize was used as a verb in 1585-95. But maybe. etymonline has “Verb womanize originally (1593) meant “to make effeminate;” sense of “to chase women, to go wenching” is attested from 1893.” But no citations for the attestation.
The etymology is interesting given that this came up in a re-run of a David Letterman piece making fun of the altogether-easy-to-make-fun-of Michael Jackson who is rumored to being remarried to yet another woman.
Any citations in OED on-line? I’d try NPA, but the OCR function is not reliable that far back.