Long-suffering cat treated with oils (7)
I believe the answer is:
stoical
'long-suffering' is the definition.
(I've seen this before)
'cat treated with oils' is the wordplay.
'treated with' indicates anagramming the letters.
'cat' anagrammed with 'oils' gives 'STOICAL'.
(Other definitions for stoical that I've seen before include "Brave in the face of pain" , "resigned to suffering" , "able to endure suffering" , "Suffering patiently" , "Uncomplaining in the face of adversity" .)