Have mounting success (3,2)

I believe the answer is:

get on

I'm a little stuck... Click here to teach me more about this clue!

'have' is the definition.
The answer and definition can be both related to bodily activities as well as being verbs in their base form.
Maybe there's an association between them I don't understand?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for get on that I've seen before include "Board - prosper" , "What boarders do" , "Hit it off" , "Proceed; prosper" , "Board vehicle or make progress" .)

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