Bird between two big roads in heat (9)
I believe the answer is:
microwave
'heat' is the definition.
(I know this)
'bird between two big roads' is the wordplay.
I cannot quite see how this works, but
'bird' could be 'crow' (crow is a kind of bird) and 'crow' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
(Other definitions for microwave that I've seen before include "(Kitchen) oven" , "Modern oven using electromagnetism" , "Kind of oven" , "Fast oven" , "Cook" .)