School yet to deal with infection (4)
I believe the answer is:
stye
'infection' is the definition.
(stye is a kind of infection)
'school yet to deal with' is the wordplay.
'school' becomes 's' (**).
'to deal with' is an anagram indicator (deal with can mean to organise or sort out).
'yet' anagrammed gives 'tye'.
's'+'tye'='STYE'
(Other definitions for stye that I've seen before include "Inflammation on eyelid" , "Observer's problem" , "Eyelid infection" , "Inflamed swelling on the edge of an eyelid" , "Eye sore" .)