Unreliable quote about a Rolls-Royce coming back (7)
I believe the answer is:
erratic
'unreliable' is the definition.
(similar in meaning)
'quote about a rolls-royce coming back' is the wordplay.
'quote' becomes 'cite' (synonyms).
'about' means one lot of letters goes inside another.
'rolls royce' becomes 'rr' (short for Rolls Royce).
'coming back' says the letters should be written backwards.
'a'+'rr'='arr'
'cite' going around 'arr' is 'citarre'.
'citarre' back-to-front is 'ERRATIC'.
(Other definitions for erratic that I've seen before include "Irregular or uneven in movement or habits" , "Shifting like Cartier" , "Unpredictable - car tire (anag)" , "Irregular, capricious" , "Irregular in pattern or movement" .)