Day came to improve college (7)
I believe the answer is:
academy
'college' is the definition.
(both can mean an educational institution)
'day came to improve' is the wordplay.
'to improve' indicates an anagram.
'day'+'came'='daycame'
'daycame' is an anagram of 'ACADEMY'.
(Other definitions for academy that I've seen before include "Secondary school" , "Centre of learning" , "training centre" , "Type of school" , "Specialist school" .)