Captain misses lessons (7)
I believe the answer is:
classes
'lessons' is the definition.
(as in school classes)
'captain misses' is the wordplay.
'captain' becomes 'c' (this might be a standard abbreviation which I don't know about).
'misses' becomes 'lasses' (lass is a kind of miss).
'c'+'lasses'='CLASSES'
Can you help me to learn more?
(Other definitions for classes that I've seen before include "See 1" , "Groups with the same social or economic status" , "Categories" .)