ran ‧ cid /ˈrænsəd, ˈrænsɪd/ BrE AmE adjective
[ Date: 1600-1700 ; Language: Latin ; Origin: rancidus , from rancere 'to have decayed, smell bad' ]
oily or fatty food that is rancid smells or tastes unpleasant because it is no longer fresh:
rancid butter