n. [ Phthalyl + anhydride. ] (Chem.) A lactone (C8H6O2) obtained as a white crystalline substance by reduction of phthalyl chloride and other processes; hence, by extension, any one of the series of which phthalide proper is the type. [ Written also phthalid. ] [ 1913 Webster ]

[ PJC ]

2. Specifically: A fungicide (C8H2Cl4O2) which is a tetrachloro derivative of phthalide{ 1 } proper; in this sense, the spelling fthalide is also used. It has CAS Registry Number 27355-22-2.
Syn. 4, 5, 6, 7-tetrachloro-1(3H)-isobenzofuranone; -- . [ PJC ]