jag (n.1)

"period of unrestrained activity," 1887, American English, perhaps via intermediate sense of "as much drink as a man can hold" (1670s), from earlier meaning "load of hay or wood" (1590s), of unknown origin. Used in U.S. colloquial speech from 1834 to mean "a quantity, a lot."

jag (n.2)

"slash or rend in a garment," c. 1400, of unknown origin.

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Definitions of jag from WordNet
jag (n.)
a sharp projection on an edge or surface;
he clutched a jag of the rock
jag (n.)
a slit in a garment that exposes material of a different color underneath; used in Renaissance clothing;
jag (n.)
a flap along the edge of a garment; used in medieval clothing;
Synonyms: dag
jag (n.)
a bout of drinking or drug taking;
jag (v.)
cut teeth into; make a jagged cutting edge;