Highland beer without cask (6)
I believe the answer is:
alpine
'highland' is the definition.
(similar in meaning)
'beer without cask' is the wordplay.
'beer' becomes 'ale' (type of beer).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'cask' becomes 'pin' (I've seen this in other clues).
'ale' going around 'pin' is 'ALPINE'.
(Other definitions for alpine that I've seen before include "Native growing up in mountainous area" , "seen in rocky state?" , "Relating to high mountains" , "Relating to a European mountain range" , "Plant of high mountains" .)