Muggins is tentatively keeping resolute (9)

I believe the answer is:

insistent

'resolute' is the definition.
(thesaurus)

'muggins is tentatively keeping' is the wordplay.
'keeping' indicates a hidden word.
'INSISTENT' is hidden in the letters of 'muggins is tentatively'.

(Other definitions for insistent that I've seen before include "Emphatic" , "Refusing to be thwarted" , "Not giving up" , "Compelling attention" , "Unwilling to take "no" for an answer" .)

I've seen this clue in The Telegraph.

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