From The Collaborative International Dictionary of English v.0.48:
Jam \Jam\, v. t. [imp. & p. p. Jammed (j[a^]md); p. pr. & vb.
n. Jamming.] [Either fr. jamb, as if squeezed between
jambs, or more likely from the same source as champ See
Champ.]
[1913 Webster]
1. To press into a close or tight position; to crowd; to
squeeze; to wedge in; to cram; as, rock fans jammed the
theater for the concert.
[1913 Webster]
The ship . . . jammed in between two rocks. --De
Foe.
[1913 Webster]
2. To crush or bruise; as, to jam a finger in the crack of a
door. [Colloq.]
[1913 Webster]
3. (Naut.) To bring (a vessel) so close to the wind that half
her upper sails are laid aback. --W. C. Russell.
[1913 Webster]
4. To block or obstruct by packing too much (people or
objects) into; as, shoppers jammed the aisles during the
fire sale.
[PJC]
5. (Radio) To interfere with (a radio signal) by sending
other signals of the same or nearby frequency; as, the
Soviets jammed Radio Free Europe broadcasts for years
during the cold war.
[PJC]
6. To cause to become nonfunctional by putting something in
that blocks the movement of a part or parts; as, he jammed
the drawer by putting in too many loose papers; he jammed
the lock by trying to pick it.
[PJC]