Obscure fellow after treatment for toes (8)
I believe the answer is:
esoteric
'obscure' is the definition.
(requiring specialist knowledge or special interest)
'fellow after treatment for toes' is the wordplay.
'fellow' becomes 'eric' (I've seen this in other clues).
'after' means one lot of letters go next to another.
'treatment for' indicates anagramming the letters (I've seen this in other clues).
'toes' anagrammed gives 'esot'.
'eric' after 'esot' is 'ESOTERIC'.
(Other definitions for esoteric that I've seen before include "Intelligible only with special knowledge" , "Mysterious to all but a chosen few" , "Aimed at a few" , "Secret kind of coteries" , "Privileged or confidential among coteries" .)