means A supreme ruler or master who holds power over lesser lords or subordinates, especially in a feudal hierarchy.

from A plain English compound, 'over' (above) plus 'lord' — itself a worn-down form of Old English 'hlafweard,' literally 'loaf-ward,' the keeper of the bread who fed the household. So an overlord is, at root, the bread-keeper standing above all the other bread-keepers: the one whose loaf outranks yours.