Green’s Dictionary of Slang

see also under grey; the spelling of gray/grey remains debatable; according to the OED there have been various choices over the years, but there seems to have been little real consistency. For the purposes of this dict., and based as far as possible on the pre-eminent style of the respective countries, ‘gray’ will be used for US terms and ‘grey’ for UK/Aus. and other ‘Commonwealth’ uses.