It's said to be high in the Hebrides (4)
I believe the answer is:
skye
'hebrides' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see an association between them that I don't see?
'it's said to be high in the' is the wordplay.
'to be high' suggests taking the first letters (I've seen 'highest of' mean this (top letter - down clues only)).
'in the' becomes 'kye' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The initial letter of 'said' is 's'.
's'+'kye'='SKYE'
Can you help me to learn more?
(Other definitions for skye that I've seen before include "Island in a boat song about Flora MacDonald and Bonnie Prince Charlie" , "Destination of a princely boat trip" , "Scotland island" , "Scots isle" , "Portree's isle" .)