1 (prec. by indef. or interrog. pron.) besides; in addition (someone else; nowhere else; who else).
2 instead; other, different (what else could I say?; he did not love her, but someone else).
3 otherwise; if not (run, (or) else you will be late).
Etymology: OE elles, rel. to L alius, Gk allos
Useful english dictionary. 2012.