The Collaborative International Dictionary of English v.0.48:

Captain \Cap"tain\ (k[a^]p"t[i^]n), n. [OE. capitain, captain,
   OF. capitain, F. capitaine (cf. Sp. capitan, It. capitano),
   LL. capitaneus, capitanus, fr. L. caput the head. See under
   Chief, and cf. Chieftain.]
   1. A head, or chief officer; as:
      (a) The military officer who commands a company, troop, or
          battery, or who has the rank entitling him to do so
          though he may be employed on other service.
      (b) An officer in the United States navy, next above a
          commander and below a commodore, and ranking with a
          colonel in the army.
      (c) By courtesy, an officer actually commanding a vessel,
          although not having the rank of captain.
      (d) The master or commanding officer of a merchant vessel.
      (e) One in charge of a portion of a ship's company; as, a
          captain of a top, captain of a gun, etc.
      (f) The foreman of a body of workmen.
      (g) A person having authority over others acting in
          concert; as, the captain of a boat's crew; the captain
          of a football team.
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                A trainband captain eke was he.   --Cowper.
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                The Rhodian captain, relying on . . . the
                lightness of his vessel, passed, in open day,
                through all the guards.           --Arbuthnot.
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   2. A military leader; a warrior.
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            Foremost captain of his time.         --Tennyson.
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   Captain general.
      (a) The commander in chief of an army or armies, or of the
          militia.
      (b) The Spanish governor of Cuba and its dependent
          islands.

   Captain lieutenant, a lieutenant with the rank and duties
      of captain but with a lieutenant's pay, -- as in the first
      company of an English regiment.
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