Third person singular present tense of 'dull'; makes something less sharp, bright, or interesting.
From 'dull' (verb form, meaning to make dull). The verb form has been in use since at least the 1500s, derived from the adjective 'dull.'
The verb 'to dull' is actually different from the adjective—when time 'dulls' your senses, you're not becoming a dull thing, you're having your sharpness taken away by time's grinding effect.
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