Crossword Genius

Certain to be clean isn't bad (13)

Ross

I believe the answer is:

incontestable

'certain' is the definition.
(thesaurus)

'to be clean isn't bad' is the wordplay.
'bad' is an anagram indicator.
'to'+'be'+'clean'+'isnt'='tobecleanisnt'
'tobecleanisnt' is an anagram of 'INCONTESTABLE'.

(Other definitions for incontestable that I've seen before include "Without doubt" , "sure" , "Beyond dispute" .)

I've seen this clue in The Telegraph.
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