Put your name down to go in (5)

I believe the answer is:

enter

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'go in' is the definition.
(synonyms)

I don't understand the rest of the clue.

(Other definitions for enter that I've seen before include "Register formally as a participant" , "Enrol" , "submit?" , "Go in - set down" , "Pierce" .)

I've seen this clue in The Globe and Mail.

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