Both are words in Hebrew. Cherubim are higher and more important then Seraphim, in the Jewish angelic hierarchy Cherubim is 5th rank (out of ten) and Seraphim only 9th.
So what I remembered I didn't even remember right. Perhaps I should brush up on my knowledge of angels.
It's different in the Christian angelic hierarchy.
http://en.wikipedia.org/wiki/Christian_angelic_hierarchyAlso, it appears that dunn got it backwards for the Jewish hierarchy.
http://en.wikipedia.org/wiki/Jewish_angelic_hierarchy