Second husband in groovy college? (6)
I believe the answer is:
school
'college?' is the definition.
(college is a kind of school)
'second husband in groovy' is the wordplay.
'second' becomes 's' (common abbreviation).
'husband' becomes 'h'.
'in' is an insertion indicator.
'groovy' becomes 'cool' (synonyms).
'h' inserted into 'cool' is 'chool'.
's'+'chool'='SCHOOL'
(Other definitions for school that I've seen before include "streaming in here?" , "Large group of fish" , "Train - a group of fish" , "A number of fish" , "Forms" .)