Definition of phenolphthalein in English:

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Pronunciation: /ˌfiːnɒlˈ(f)θaliːn/
Pronunciation: /ˌfiːnɒlˈ(f)θeɪliːn/


[mass noun] Chemistry
A colourless crystalline solid (pink in alkaline solution) used as an acid-base indicator and medicinally as a laxative.
  • Chemical formula: C20H14O4.
Example sentences
  • The maintenance phase consisted of ‘Agarol’ (active ingredients: liquid paraffin, phenolphthalein, benzoic acid, and sorbic acid) 5-30 ml once or twice daily, senna granules, or bisacodyl tablets.
  • The non-osmotic laxatives, phenolphthalein and senna, partly act by stimulating secretory mechanisms in the intestine.
  • The listing is based on findings from feeding studies of phenolphthalein that caused cancer in multiple organs in multiple species of experimental animals.


Late 19th century: from phenol + -phthal- (from naphthalene) + -in1.

For editors and proofreaders

Line breaks: phe¦nol|phthal¦ein

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