Walk one in pram, mostly before noon (13)

I believe the answer is:

perambulation

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'walk' is the definition.
(I know that perambulation is a type of walk)

I don't understand the rest of the clue.

(Other definitions for perambulation that I've seen before include "Action of walking around" , "Process of walking" .)

I've seen this clue in The Times.

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