1. [early–mid-19C] absolutely defeated.
2. [early 19C+] worn out, exhausted [note Egan, Life in London (1821): ‘“Dead beat!” or “beat to a stand still!” Common phrases in the Sporting World, when a man or horse is so completely exhausted from over-exertion, or the constitution breaking down, as to give up the object in view, not being able to pursue it any further’].
3. [mid-19C] lazy, idle.
4. [late 19C+] useless, ne’er-do-well, impoverished.