Say yew outside old church is poetic feature (7)
I believe the answer is:
trochee
'poetic feature' is the definition.
(type of metrical foot in poetry)
'say yew outside old church' is the wordplay.
'say yew' becomes 'tree' (yew is a type of tree).
'outside' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'church' becomes 'ch' (common abbreviation).
'o'+'ch'='och'
'tree' enclosing 'och' is 'TROCHEE'.
'is' acts as a link.
(Other definitions for trochee that I've seen before include "To cheer about this metrical unit" , "service, for example" , "Long-short foot in poetry" , "Long-short metric foot" , "Long-short metrical foot" .)