Coastal feature, unique, captivating husband (7)
I believe the answer is:
shingle
'coastal feature' is the definition.
'unique captivating husband' is the wordplay.
'unique' becomes 'single' ('single' can be similar in meaning to 'unique').
'captivating' means one lot of letters goes inside another (I've seen this in other clues).
'husband' becomes 'h'.
'single' enclosing 'h' is 'SHINGLE'.
(Other definitions for shingle that I've seen before include "A mass of seashore pebbles" , "Gravelly composition" , "'hairdo'" , "Loose stones" , "Water-worn pebbles - roofing tile" .)