Green’s Dictionary of Slang

cray n.²

[it is coloured red, like the SE crayfish]

(N.Z.) a NZ$100 note.

1988		McGill Dict. of Kiwi Sl. 31/2: cray 100 dollar bill; from its colour red, same as a crayfish.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].