He's less than benign (3)
I believe the answer is:
ben
'he's' is the definition.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ben that I've seen before include "A Scottish mountain like Nevis" , "inner room in Oban, say" , "Boy for a Scottish mountain" , "Mountain; man's name" , "High mountain (Scots)" .)