Haha! Thematic vowel (e/o)! Tell us more.

Well, there are two kinds of verbs in IE languages: thematic and athematic, with two associated sets of personal endings. In Latin, you've got 4 conjugations: -are, -e:re, -ere, -ire. Basically, Latin simplified the system to just thematic systems using -o, -Vs, -Vt, etc. for endings. Sanskrit used the athematic endings: -mi, -si, -ti, etc. Greek uses both: some verbs end in -o: and others in -mi. For the motion verb above, there's actually two different verbs: kineo: vs kineumi. (There's also another interesting thing about these verbs, in that they show evidence of the nasal presents: a whole other thing.) Anyway, it's a lot harder than my simplistic explanation, but a good book to look at, still in print I think, is W. Lehmann's Theoretical Bases of Indo-European Linguistics. The reason I wrote the vowel as e/o, is that depending on where the accent (or tone) of a word falls, an /e/ sometimes becomes an /o/. These thematic vowels probably started out as a kind of suffix that changed the meaning of the verb.