Rarefied ground or site retained by English clubs (8)
I believe the answer is:
esoteric
'rarefied' is the definition.
(I've seen this in another clue)
'ground or site retained by english clubs' is the wordplay.
'ground' indicates anagramming the letters ('grind' the letters into a new form).
'retained by' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'or'+'site'='orsite'
'orsite' anagrammed gives 'soteri'.
'e'+'c'='ec'
'soteri' inserted inside 'ec' is 'ESOTERIC'.
(Other definitions for esoteric that I've seen before include "of rarefied tastes" , "Intended for the few" , "Taught to a select few" , "Occult" , "Abstruse; secret" .)