WordNet (r) 3.0 (2006):

Cain
    n 1: (Old Testament) Cain and Abel were the first children of
         Adam and Eve born after the Fall of Man; Cain killed Abel
         out of jealousy and was exiled by God

Easton's 1897 Bible Dictionary:

Cain
   a possession; a spear. (1.) The first-born son of Adam and Eve
   (Gen. 4). He became a tiller of the ground, as his brother Abel
   followed the pursuits of pastoral life. He was "a sullen,
   self-willed, haughty, vindictive man; wanting the religious
   element in his character, and defiant even in his attitude
   towards God." It came to pass "in process of time" (marg. "at
   the end of days"), i.e., probably on the Sabbath, that the two
   brothers presented their offerings to the Lord. Abel's offering
   was of the "firstlings of his flock and of the fat," while
   Cain's was "of the fruit of the ground." Abel's sacrifice was
   "more excellent" (Heb. 11:4) than Cain's, and was accepted by
   God. On this account Cain was "very wroth," and cherished
   feelings of murderous hatred against his brother, and was at
   length guilty of the desperate outrage of putting him to death
   (1 John 3:12). For this crime he was expelled from Eden, and
   henceforth led the life of an exile, bearing upon him some mark
   which God had set upon him in answer to his own cry for mercy,
   so that thereby he might be protected from the wrath of his
   fellow-men; or it may be that God only gave him some sign to
   assure him that he would not be slain (Gen. 4:15). Doomed to be
   a wanderer and a fugitive in the earth, he went forth into the
   "land of Nod", i.e., the land of "exile", which is said to have
   been in the "east of Eden," and there he built a city, the first
   we read of, and called it after his son's name, Enoch. His
   descendants are enumerated to the sixth generation. They
   gradually degenerated in their moral and spiritual condition
   till they became wholly corrupt before God. This corruption
   prevailed, and at length the Deluge was sent by God to prevent
   the final triumph of evil. (See ABEL.)

     (2.) A town of the Kenites, a branch of the Midianites (Josh.
   15:57), on the east edge of the mountain above Engedi; probably
   the "nest in a rock" mentioned by Balaam (Num. 24:21). It is
   identified with the modern Yekin, 3 miles south-east of Hebron.


Hitchcock's Bible Names Dictionary (late 1800's):

Cain, possession, or possessed