Patience tried endlessly as oil wasted (9)
I believe the answer is:
solitaire
'patience' is the definition.
('solitaire' can be a synonym of 'patience')
'tried endlessly as oil wasted' is the wordplay.
'endlessly' means to remove the last letter.
'wasted' indicates an anagram.
'tried' with its last letter taken off is 'trie'.
'trie'+'as'+'oil'='trieasoil'
'trieasoil' with letters rearranged gives 'SOLITAIRE'.
(Other definitions for solitaire that I've seen before include "songbird" , "Single stone in jewellery" , "Gem set by itself" , "recluse" , "Bond girl" .)