noun
Usage: usually capitalized N
Etymology: German naphthol AS, from naphthol + AS, from a nilid anilide + s äure acid
1. : a crystalline phenolic anilide HOC 10 H 6 CONHC 6 H 5 used as a coupling component for azoic dyes; the anilide of 3-hydroxy-2-naphthoic acid — see dye table I (under Azoic Coupler 2 )
2. : any of a series of arylides of either ortho -hydroxy aromatic carboxylic acids (as 3-hydroxy-2-naphthoic acid) or acyl derivatives (as acetoacetic acid) of acetic acid used as coupling components for azoic dyes — see dye table I (under Azoic Coupler )