What is "get the sack"

Sack \Sack\, n. [OE. sak, sek, AS. sacc, s[ae]cc, L. saccus, Gr. sa`kkos from Heb. sak; cf. F. sac, from the Latin. Cf. Sac, Satchel, Sack to plunder.]

1. A bag for holding and carrying goods of any kind; a receptacle made of some kind of pliable material, as cloth, leather, and the like; a large pouch.

2. A measure of varying capacity, according to local usage and the substance. The American sack of salt is 215 pounds; the sack of wheat, two bushels.
   --McElrath.

3. [Perhaps a different word.] Originally, a loosely hanging garment for women, worn like a cloak about the shoulders, and serving as a decorative appendage to the gown; now, an outer garment with sleeves, worn by women; as, a dressing sack. [Written also sacque.]

4. A sack coat; a kind of coat worn by men, and extending from top to bottom without a cross seam.

5. (Biol.) See 2d Sac, 2.

6. Bed. [Colloq.]

   Sack bearer (Zo["o]l.). See Basket worm, under Basket.

   Sack tree (Bot.), an East Indian tree ( Antiaris saccidora) which is cut into lengths, and made into sacks by turning the bark inside out, and leaving a slice of the wood for a bottom.

   To give the sack to or get the sack, to discharge, or be discharged, from employment; to jilt, or be jilted.

   To hit the sack, to go to bed. [Slang]

vb. (context idiomatic chiefly British English) To be dismissed from employment.