Department in minor seaside town (8)
I believe the answer is:
yarmouth
'seaside town' is the definition.
'department in minor' is the wordplay.
'department' becomes 'arm' (both can mean a division of an organisation).
'in' means one lot of letters goes inside another.
'minor' becomes 'youth'.
'arm' going inside 'youth' is 'YARMOUTH'.
(Other definitions for yarmouth that I've seen before include "holiday resort" , "Isle of Wight town (Great in Norfolk)" , "Norfolk resort" , "27 [ISLAND] town" , "IOW port" .)