noun
1. often capitalized O&Y
a. : any of several oil-soluble yellow dyes : see dye table I (under Solvent Yellow )
b. or oil yellow II : a carcinogenic azo dye C 6 H 5 N 2 C 6 H 4 N(CH 3 ) 2 formerly used in coloring butter and oils; para -dimethyl-aminoazobenzene — called also butter yellow, methyl yellow ; see dye table I (under Solvent Yellow 2 )
2. : a moderate greenish yellow that is greener and duller than citron yellow and deeper than linden green