Which side of shoe is uncomfortable? (4)
I believe the answer is:
sore
'uncomfortable?' is the definition.
(synonyms)
'which side of shoe' is the wordplay.
'which' becomes 'sor' (I can't explain this - if you can you should give a lot more credence to this answer).
'side of' says to take the final letters.
The final letter of 'shoe' is 'e'.
'sor'+'e'='SORE'
'is' acts as a link.
(Other definitions for sore that I've seen before include "To be very old" , "Painfully sensitive" , "Irritated or painful" , "very much" , "Hard" .)