any compound derived from phenol by the replacement of one or more of its ring hydrogen atoms by the nitro group

any of three water-soluble, crystalline isomers of such a derivative, having the formula C6H5NO3, occurring in yellow (ortho-nitrophenol), pale-yellow (meta-nitrophenol), and yellowish (para-nitrophenol) solids, used chiefly as intermediates in organic synthesis and as indicators