From The Collaborative International Dictionary of English v.0.48 [gcide]:
Ogre \O"gre\ ([=o]"g[~e]r), noun [F., fr. Sp. ogro, fr. L. Orcus the god of the infernal regions; also, the lower world, hell.] An imaginary monster, or hideous giant of fairy tales, who lived on human beings; hence, any frightful giant; a cruel monster.
From WordNet (r) 3.0 (2006) [wn]:
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