Definition of rarest:
(adj) :
Very uncommon; scarce.
(adj) :
(medicine, pathology) Small in number (but not unusual); infrequent; sparse.
(adj) :
(cooking) Particularly of meat, especially beefsteak: cooked very lightly, so the meat is still red.
(n) :
(gaming) A scarce or uncommon item.
(adj) :
(UK, slang) Good; enjoyable.
(adj) :
(of a gas) Thin; of low density.