imperative particle
Definition - The words do, don't, let, and let's when used in the imperative, e.g. Do tell me, Don't tell me, Let me see now, and Let's go.

Example Usages -

1. "Among individual words commonly so classed are the negative particle not (and its contraction n't), the infinitival particle to (to go; to run), the imperative particles do, don't (Do tell me; Don't tell me) and let, let's (Let me see now; Let's go)."
(Source: Sidney Greenbaum, Oxford Companion to the English Language s.v. particle )

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