Cross mouth of Tay to get to Dundee? (7)
I believe the answer is:
tangelo
'cross' is the definition.
(cross-bred fruit)
'mouth of tay to get to dundee?' is the wordplay.
'mouth of' says to take the initial letters (mouth can mean something's origin).
'to get' says to put letters next to each other.
'to dundee?' becomes 'Angelo' (boxing coach Angelo Dundee).
The initial letter of 'tay' is 't'.
't'+'angelo'='TANGELO'
(Other definitions for tangelo that I've seen before include "one cross, sour" , "fruitful merger?" , "Mixed fruit" , "Citrus hybrid - goal net (anag)" , "Hybrid fruit; eat long (anag.)" .)