In trademark law, the more unusual a term, the more it qualifies for protection. We would have no quarrel with Marvel and DC had they called their superheroes "actosapiens," then trademarked that. But purely generic terms aren't entitled to protection, at least in theory. The reason is simple: Trademarks restrict speech, and to put widely used terms under private control is an assault on our language.
(Link via Neilalien.)