Understood by few (6)
'understood by few' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for esoteric that I've seen before include "Hard to understand" , "Understandable by only an enlightened inner circle" , "Aimed at a few" , "Private, confined to a select group" , "Occult" .)
'understood by few' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for arcane that I've seen before include "Ace ran, being mysterious" , "Mysterious, understood by few" , "Mysterious - an acre (anag)" , "Recondite" , "Requiring special knowledge" .)