Crossword Genius

Make sure of showing sectarian trouble (9)

Ross

I believe the answer is:

ascertain

'make sure of' is the definition.
(thesaurus)

'sectarian trouble' is the wordplay.
'trouble' is an anagram indicator.
'sectarian' is an anagram of 'ASCERTAIN'.

'showing' acts as a link.

(Other definitions for ascertain that I've seen before include "Become aware" , "Find out for sure, determine" , "Verify" , "Establish (the facts)" , "Establish after an investigation or study" .)

I've seen this clue in The Independent.
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