Simple derivational etymology deriving the longer word from the shorter one. It is correct my modern standards but runs contrary to Herodian's doctrine which reverses the derivation and teaches that κἀρα or κάρη is derived from κάρανον κάρηνον. Therefore it is seldom found in our sources, whereas Herodian's doctrine is repeated by all grammarians and all lexicographers (see κάρα / κάρηνον). The sources transmitting this derivation give Herodian's explanation, too