Thayer's Greek Lexicon

 1. the altar for slaying and burning of victims used of
  1) the altar of whole burnt offerings which stood in the court of
the priests in the temple at Jerusalem
  2) the altar of incense which stood in the sanctuary or the Holy Place
  3) any other altar
1c1. metaph., the cross on which Christ suffered an expiatory
death: to eat of this altar i.e. to appropriate to one's
self the fruits of Christ's expiatory death