Can you hear it turn in the air? (4)
I believe the answer is:
tern
'can you hear it turn' is the definition.
I can't tell whether this definition defines the answer.
'the air?' is the wordplay.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'air?' becomes 'ern' (I am not sure about this - if you are sure you should believe this answer much more).
't'+'ern'='TERN'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for tern that I've seen before include "Small slender gull" , "Pay rent for seabird" , "Rent out the bird" , "Sea bird, a small gull" , "Seagull" .)