from The American Heritage® Dictionary of the English Language, 4th Edition
- n. One that is expected to lose a contest or struggle, as in sports or politics.
- n. One that is at a disadvantage.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A competitor thought unlikely to win.
- n. Somebody at a disadvantage.
- n. A high swing wherein the person pushing the swing runs beneath the swing while the person being pushed is at the forward limit of the arc.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. one at a disadvantage and expected to lose
From under + dog. (Wiktionary)