Coastal feature of great height, it would seem! (5)
I believe the answer is:
bight
'coastal feature' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'great height it would seem' is the wordplay.
I cannot quite see how this works, but
'great' could be 'big' (synonyms) and 'big' is located in the answer.
'height' could be 'ht' (abbreviation) and 'ht' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for bight that I've seen before include "Curve of shore" , "Coastline curve forming a bay" , "bend in river" , "loop of rope?" , "Bay, sounds like a morsel of food" .)