Third person singular present tense; means to spend too much effort or time on something, or to explain something in excessive detail.
From 'belabor,' which combines Old English 'be-' (to make or cover thoroughly) with 'labor.' The '-s' suffix marks third-person singular present tense in English.
This is the form you'd use when talking about someone else: 'She belabors every point in class'—it's the grammatical way of describing someone else's habit of over-explaining!
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