To allow or permit someone to do something. In some varieties of English, it can also mean to rent out a house or room.
From Old English *lǣtan* meaning “to allow, let go, or leave,” related to German *lassen* (to let, allow). Interestingly, there was also an older sense meaning “to hinder,” now mostly gone except in set phrases.
English once had two nearly opposite ‘let’ verbs: one meant “allow,” the other meant “hinder”—a nightmare for learners. A fossil of the old ‘hinder’ meaning survives in tennis, where a ‘let’ is a serve that doesn’t quite count.
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