Definition of Naphthol AS
1
: a crystalline phenolic anilide HOC10H6CONHC6H5 used as a coupling component for azoic dyes; the anilide of 3-hydroxy-2-naphthoic acid
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
