The only other usage than "horsing around" I can find on a (SafeSearch) Google, is the expression "to horse a gentlewoman", which I assume is an historical expression meaning the general assistance of a lady in enabling her to ride out. Then again, maybe I'm being naïve and it has a more Catherine the Great connotation.
I believe it involves a carpenter's sawhorse (suitably reinforced and stabilised), a willing 'victim', a quantity of rope and a good imagination. It might be a good idea to keep a chiropracter on the speed dialer too IMHO.
Earlier today something similar to Projoy's comment on "thicken" occurred to me, although I noted that "enlarge" seems to apply the suffix as a prefix. There are words such as "enliven" which seem to follow the same pattern, except "liven" isn't an adjective (at least now). Anyone know a reason why "enlarge" behaves like that?
[Darren] No idea, but it did make me think of the verb from "bold" is "to embolden", which has both suffix and prefix (though not necessarily in that order).