"loon" in the noun sense
1. loon
a worthless lazy fellow
2. loon, diver
large somewhat primitive fish-eating diving bird of the northern hemisphere having webbed feet placed far back related to the grebes
3. addle-head, addlehead, loon, birdbrain
a person with confused ideas incapable of serious thought
Source: WordNet® (An amazing lexical database of English)
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