There's no limit to legitimacy of one who is guarded (5)

I believe the answer is:

cagey

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'is guarded' is the definition.
(thesaurus)

I can't explain the rest of the clue.

(Other definitions for cagey that I've seen before include "not open" , "Secretive, cautious about giving information" , "Keeping things to oneself" , "reluctant to give information" , "guarded" .)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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