Participates in, as one promises to (7)

I believe the answer is:

engages

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'participates' is the definition.
The answer and definition can be both to do with social activities as well as being verbs in their -s form.
Maybe there's an association between them I don't understand?

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for engages that I've seen before include "Employs, hires" , "books" .)

I've seen this clue in the Evening Standard.

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