Discussion Forum—A Way with Words, a fun radio show and podcast about language

I was looking through Funk & Wagnalls New Practical Standard Dictionary and for the lemma tomboy the etymology given is: [Tom + boy]. Now, that may mean nothing per se, but it is significant that there are two different lemmata spelt t-o-m: one meaning a male of a species and the other meaning Thomas. It is to the latter that the etymology points and not the former (since the etymology capitalizes the tom). So, I'm wondering if it isn't a pleonasm afterall. That is, perhaps there was once a girl named Thomasina who was a bit too hoyden and consequently left her namesake as a reminder (and perhaps as a stern warning). I know, that sounds far-far-fetched but, who knows… Otherwise, why not just apply it to boys only, if it is twice masculine?