Big Ben (5)
I believe the answer is:
nevis
'ben' is the definition.
(I have seen 'Highest Ben' mean 'nevis' so perhaps 'ben' could also mean 'nevis')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for nevis that I've seen before include "Ben -, highest British mountain" , "The principal ben" , "Ben -, highest Br. spot" , "Ben ..... is highest mountain in Britain" , "Island" .)