School yet to deal with swelling (4)
I believe the answer is:
stye
'swelling' is the definition.
(stye is a kind of swelling)
'school yet to deal with' is the wordplay.
'school' becomes 's' ().
'to deal with' indicates anagramming the letters (to deal with can mean to tidy up or sort out).
'yet' with letters rearranged gives 'tye'.
's'+'tye'='STYE'
(Other definitions for stye that I've seen before include "makes viewer sore" , "Infection on the edge of the eye" , "It pains viewer" , "Swelling near the eye" , "Eye sore" .)