Real Dictionary

alizarin in American English
a reddish-yellow crystalline compound, C6H4(CO)2C6H2(OH)2, produced by oxidizing anthracene and used in dyeing wool, cotton, and silk and in the manufacture of dyestuffs: it was originally made from madder
noun: a solid appearing reddish-orange as crystals and brownish-yellow as powder, C14H8 O4, one of the earliest known dyes, formerly obtained in its natural state from madder and now derived from anthraquinone: used chiefly in the synthesis of other dyes

alizarin in British English
noun: a brownish-yellow powder or orange-red crystalline solid used as a dye and in the manufacture of other dyes. Formula: C6 H4(CO)2C6H2(OH)2