Without a beard; smooth-faced; or figuratively, young, inexperienced, or lacking maturity (as beards traditionally signified age and wisdom).
From Middle English 'berd' (beard) with the negation suffix '-less' (without). Shakespeare used this term to suggest youth and immaturity.
In Shakespeare's time, 'beardless' was an insult implying you were too young to have wisdom—today nobody cares, showing how completely social meanings of facial hair have shifted!
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