Stout aunt's off to church (7)
I believe the answer is:
staunch
'stout' is the definition.
(thesaurus)
'aunt's off to church' is the wordplay.
'off' is an anagram indicator.
'to church' becomes 'ch' (common abbreviation).
'aunts' is an anagram of 'staun'.
'staun'+'ch'='STAUNCH'
(Other definitions for staunch that I've seen before include "act to stop bleeding" , "Very loyal, committed" , "solid" , "Plug" , "way to limit bloodshed" .)