jinnit, n. — Green’s Dictionary of Slang

jinnit n.

[Sp. jinete, a light horseman]

(Irish) a mule.

1722		N. Browne ‘North Country Wedding’ in A. Carpenter Verse in Eng. in 18C Ireland (1998) 130: The bride, the fairest of the Female-Throng, / Up-mounted sat upon a Jennet fair.
1997		Share Slanguage.

act the jinnit (v.)

(Irish) to play the fool, to act irrationally.

1997