What is "phthalide"

Phthalide \Phthal"ide\, n. [Phthalyl + anhydride.] (Chem.) A lactone obtained by reduction of phthalyl chloride, as a white crystalline substance; hence, by extension, any one of the series of which phthalide proper is the type. [Written also phthalid.]

n. (context organic chemistry English) phthalein

Phthalide is an organic chemical compound with the molecular formula CHO. It is a lactone that serves as the core chemical structure for a variety of more complex chemical compounds including dyes (such as phenolphthalein), fungicides (such as tetrachlorophthalide, often referred to simply as "phthalide") and natural oils (such as butylphthalide).