Fruit foreign to a glen (7)
I believe the answer is:
tangelo
'fruit' is the definition.
(I know that tangelo is a fruit)
'foreign to a glen' is the wordplay.
'foreign' indicates anagramming the letters (foreign order of the letters).
'to'+'a'+'glen'='toaglen'
'toaglen' is an anagram of 'TANGELO'.
(Other definitions for tangelo that I've seen before include "Mixed fruit" , "Citrus fruit hybrid" , "sharp cross" , "fruitful merger?" , "Hybrid fruit; eat long (anag.)" .)