Reddish church at top of hill (6)
I believe the answer is:
cerise
'reddish' is the definition.
(thesaurus)
'church at top of hill' is the wordplay.
'church' becomes 'ce' (abbreviation for Church of England).
'at top of' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'hill' becomes 'rise' (both can mean raised ground).
'ce'+'rise'='CERISE'
(Other definitions for cerise that I've seen before include "Cherry-coloured" , "EEC, sir, is red" , "Light red colour" , "Reddish-pink colour" , "Shade of red" .)