ester

noun

es·​ter ˈe-stər 

: any of a class of often fragrant organic compounds that can be represented by the formula RCOOR′ and that are usually formed by the reaction between an acid and an alcohol with elimination of water

Examples of ester in a Sentence

Recent Examples on the Web

Your Body Isn't Absorbing It The supplements in ethyl ester capsules are also poorly absorbed, reducing efficacy. —Ayesha Gulzar, Verywell Health, 6 May 2026

This enzyme cleaves the ester bonds in the neuronal portion of the back retina—the retinal pigment epithelium— to create a usable form of vitamin A, a molecule called 11-cis-retinal. —Lauren J. Young, Scientific American, 4 May 2026

Plus, xylitol esters help to further reduce odor-causing bacteria from adhering to the skin. —Conçetta Ciarlo, Vogue, 29 Mar. 2026

The formula leans on a retinoid ester, a milder cousin in the retinoid family that converts into retinoic acid through several metabolic steps. —Christa Joanna Lee, Allure, 23 Jan. 2026

Word History

Etymology

German, from Essigäther ethyl acetate, from Essig vinegar + Äther ether

First Known Use

circa 1852, in the meaning defined above

Rhymes for ester

• esther
• fester
• jester
• nester
• nestor
• pester
• prester
• quaestor
• tester
• wester
• yester
• ancestor

Kids Definition

ester

noun

es·​ter ˈes-tər 

: an organic compound formed by the reaction between an acid and an alcohol

Medical Definition

ester

noun

es·​ter ˈes-tər 

: any of a class of often fragrant compounds that can be represented by the formula RCOOR′ and that are usually formed by the reaction between an acid and an alcohol usually with elimination of water