Similar and seem

Come from the same IE root, but the former got Latinized. The IE is *sem- "together". Butduring latinization it got a formal verb ending, likely in late Latin. The original IE root was in early Latin.

semejar - Spanish for look alike fro *sem-.  The past participle semajado.

But the Spanish borrowed back 'similar' from English for similar.  *sem- goes way back, evidently an easy way for the IE people to tell two or more people to get anything done.