[fee-nawl-thal-een, -ee-in, -fthal-, -nol-]

noun Chemistry, Pharmacology.

a white, crystalline compound, C20H14O4, used as an indicator in acid-base titration and as a laxative.

Origin of phenolphthalein

First recorded in 1870–75; phenol + phthalein Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for phenolphthalein

Historical Examples of phenolphthalein

  • Mix the saccharin with the tincture of vanilla, and incorporate the phenolphthalein.

    Candy Medication

    Bernard Fantus

  • Phenolphthalein as shown above is not a good indicator for this purpose.

    The Fundamentals of Bacteriology

    Charles Bradfield Morrey

  • A solution of phenolphthalein loses its color when an acid is added to it.

    A Civic Biology

    George William Hunter

  • If only perfectly fresh milk is used, the amount of acid will generally be about 0.15 per cent with phenolphthalein as indicator.

  • When dark colored oils or fats are being titrated it is often difficult to obtain a good end point with phenolphthalein.

    Soap-Making Manual

    E. G. Thomssen

British Dictionary definitions for phenolphthalein



a colourless crystalline compound used in medicine as a laxative and in chemistry as an indicator. Formula: C 20 H 14 O 4
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

phenolphthalein in Medicine


[fē′nōl-thălēn′, -thălē-ĭn, -thālēn′, -thālē-ĭn]


A white or pale yellow crystalline powder that is used as an acid-base indicator and a laxative.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

phenolphthalein in Science



A white or pale-yellow, crystalline powder used as an indicator for acid and basic solutions. In solutions that are either neutral or basic, it is colorless, while it is pink or red in solutions that are alkali. It is also used as a laxative and in making dyes. Chemical formula: C20H14O4.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.