The word "fortasse" (meaning 'perhaps') looks like it's two words squished together, but I can't find any etymology for it. Does anyone know where fortasse comes from?
It comes from forte "perhaps", which seems to be from the ablative of fors "chance, luck" (Proto-Indo-European root *bʰr-ti- 'bearing, case'). That in turn is derived from the same root as fero "to bring" (Proto-Indo-European *bʰer-e/o- 'to carry', De Vaan s.v.).
De Vaan s.v. fors:
PIE *bʰr-ti- 'bearing, case'? IE cognates: see s.v.ferō
The origin of fortasse seems to be *forte an sīt/s, but the phonetics (especially the short final vowel) are unclear.
Forte an sit would mean something like "[it is] chance whether that is [so]". Cf. forsitan, fortassean.