Cold air teacher's struggling to describe (12)
I believe the answer is:
characterise
'describe' is the definition.
(characterise can mean to describe in a certain way)
'cold air teacher's struggling' is the wordplay.
'cold' becomes 'c' (eg on taps).
'struggling' indicates an anagram.
'air'+'teachers'='airteachers'
'airteachers' is an anagram of 'haracterise'.
'c'+'haracterise'='CHARACTERISE'
'to' is the link.
(Other definitions for characterise that I've seen before include "Be a distinctive feature of" , "Typify" , "Describe" .)