Jam, n. — Webster enters it under “jam”
Etymology: [Per. or Hind. jamah garment, robe.]
A kind of frock for children.
4 other Webster entries under this spelling
Jam, n. (Mining)
See Jamb.
Jam, v. t. [imp. & p. p. Jammed; p. pr. & vb. n. Jamming.]
1. To press into a close or tight position; to crowd; to squeeze; to wedge in. The . . . jammed in between two rocks. De Foe.
2. To crush or bruise; as, to jam a finger in the crack of a door. [Colloq.]
3. (Naut.)
To bring (a vessel) so close to the wind that half her upper sails are laid aback. W. C. Russell.
Jam, n.
1. A mass of people or objects crowded together; also, the pressure from a crowd; a crush; as, a jam in a street; a jam of logs in a river.
2. An injury caused by jamming. [Colloq.]
Jam, n.
A preserve of fruit boiled with sugar and water; as, raspberry jam; currant jam; grape jam. Jam nut. See Check nut, under Check. -- Jam weld (Forging), a butt weld. See under Butt.
Shades of meaning
Fernald lists jammed only as an antonym, under vacant.
He lists it without comment; the entries above explain its neighbors.