What is "to train a gun"

Train \Train\, v. t. [imp. & p. p. Trained; p. pr. & vb. n. Training.] [OF. trahiner, tra["i]ner,F. tra[^i]ner, LL. trahinare, trainare, fr. L. trahere to draw. See Trail.]

1. To draw along; to trail; to drag.

   In hollow cube Training his devilish enginery.
   --Milton.

2. To draw by persuasion, artifice, or the like; to attract by stratagem; to entice; to allure. [Obs.]

   If but a dozen French Were there in arms, they would be as a call To train ten thousand English to their side.
   --Shak.

   O, train me not, sweet mermaid, with thy note.
   --Shak.

   This feast, I'll gage my life, Is but a plot to train you to your ruin.
   --Ford.

3. To teach and form by practice; to educate; to exercise; to discipline; as, to train the militia to the manual exercise; to train soldiers to the use of arms.

   Our trained bands, which are the trustiest and most proper strength of a free nation.
   --Milton.

   The warrior horse here bred he's taught to train.
   --Dryden.

4. To break, tame, and accustom to draw, as oxen.

5. (Hort.) To lead or direct, and form to a wall or espalier; to form to a proper shape, by bending, lopping, or pruning; as, to train young trees.

   He trained the young branches to the right hand or to the left.
   --Jeffrey.

6. (Mining) To trace, as a lode or any mineral appearance, to its head.

   To train a gun (Mil. & Naut.), to point it at some object either forward or else abaft the beam, that is, not directly on the side.
   --Totten.

   To train, or To train up, to educate; to teach; to form by instruction or practice; to bring up.

   Train up a child in the way he should go; and when he is old, he will not depart from it.
   --Prov. xxii. 6.

   The first Christians were, by great hardships, trained up for glory.
   --Tillotson.