Thayer's Greek Lexicon

 1. the head, both of men and often of animals. Since the loss of the
head destroys life, this word is used in the phrases relating to
capital and extreme punishment.
2. metaph. anything supreme, chief, prominent
  1) of persons, master lord: of a husband in relation to his wife
  2) of Christ: the Lord of the husband and of the Church
  3) of things: the corner stone