As I was publishing this post from John Maloney, I thought I would look up the word gig ... it makes for an interesting read.
A child's pacifier or any object, as a cloth square, spoon, or the like, used as a toy; any object to which a small child is attached and with which he likes to play; any object treated by a child as a fetish; a gigi or ju-ju. Orig. Negro slave and Southern use. From "gigi," the word is very well known to about 35% of the population, unheard of by the rest.
The rectum. From "gigi." Used euphem. by some children, as part of their bathroom vocabulary, but not common to all children. Used by some male adults [taboo] as a euphem. for "ass" in such expressions as "up your gig." 3 [taboo] The vagina. From "gigi." Not common. Prob. Southern use.
A party, a good time; esp. an uninhibited party; occasionally but not often, an amorous session, necking party, or even a sexual orgy between a man and a woman. c1915 : "Cornet players used to pawn their instruments when there was a lull in funerals, parades, dances, gigs and picnics." L. Armstrong, Satchmo, My Life in New Orleans, 100. 1958: "Life is a Many Splendored Gig," a song title.
A jam session ; a jazz party or gathering of jazz musicians or enthusiasts. Orig. swing use. 1920 : "Kid Ory had some of the finest gigs, especially for the rich white folk." L. Armstrong, Satchmo, My Life in New Orleans, 141.
An engagement or job for a jazz musician or musicians, esp. for a one-night engagement. 1950: "If I ask you to go out on a gig, it's thirty-five or forty dollars for that night." A. Lomax, Mr. Jelly Roll, 204. 1954: "On a gig, or one night stand." L. Armstrong, Satchmo, My Life in New Orleans, 221.
Something, as a jazz arrangement, that is satisfying or seems perfect. Orig. swing use.
An unfavorable report; a demerit; a reprimand. Army and some student use since c1940. The relations, if, any, between a child's pacifier or fetish, the rectum and vagina, a party, a sex orgy, jazz music, a pronged fork, and a reprimand are most interesting, and lie in the field of psychology rather than of etymology.
A fishing spear; a pronged fork as used for catching fish, frogs, and the like.
etc .... they forgot this one: