Stop male, one in natural setting that’s undefined (13)
I believe the answer is:
indeterminate
'that's undefined' is the definition.
(thesaurus)
'stop male one in natural' is the wordplay.
I cannot quite understand how this works, but
'stop' could be 'terminate' (terminate can mean to stop or bring to an end) and 'terminate' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'setting' is the link.
Can you help me to learn more?
(Other definitions for indeterminate that I've seen before include "Unspecified" , "Not precisely fixed" , "Vague - unsettled" , "Having no fixed value" , "Inconclusive" .)