insoluble

adjective

in·​sol·​u·​ble (ˌ)in-ˈsäl-yə-bəl 

: not soluble: such as

a

: incapable of being dissolved in a liquid and especially water

also : soluble only with difficulty or to a slight degree

b

: having or admitting of no solution or explanation

an insoluble problem

c

archaic : indissoluble

insolubility

(ˌ)in-ˌsäl-yə-ˈbi-lə-tē 

noun

insoluble noun

insolubleness

(ˌ)in-ˈsäl-yə-bəl-nəs 

noun

insolubly

(ˌ)in-ˈsäl-yə-blē 

adverb

Synonyms of insoluble

• impossible
• hopeless

Examples of insoluble in a Sentence

a substance insoluble in water

the seemingly insoluble mystery concerning the identity of the people who built these ancient structures

Recent Examples on the Web

Key sources of fiber, both soluble and insoluble, include seeds, beans, lentils, whole grains and vegetables. —Kaitlin Sullivan, NBC news, 29 Apr. 2026

The seeds are rich in both soluble and insoluble fiber, helping to feed gut bacteria while also promoting regular bowel movements, research has shown. —Deirdre Bardolf, FOXNews.com, 27 Apr. 2026

Wheat bran is primarily insoluble fiber with a little protein, fat and phenolic compounds. —The New York Times News Service Syndicate, San Diego Union-Tribune, 15 Apr. 2026

Whole wheat bread is rich in insoluble fiber, which helps prevent digestive constipation. —Lindsay Curtis, Health, 9 Apr. 2026

Word History

Etymology

Middle English insolible, from Latin insolubilis, from in- + solvere to free, dissolve — more at solve

First Known Use

14th century, in the meaning defined above

Rhymes for insoluble

• soluble
• voluble
• indissoluble
• revoluble

Kids Definition

insoluble

adjective

in·​sol·​u·​ble (ˈ)in-ˈsäl-yə-bəl 

1

: impossible to solve

an insoluble problem

2

: impossible or difficult to dissolve

a substance insoluble in water

Medical Definition

insoluble

adjective

in·​sol·​u·​ble (ˈ)in-ˈsäl-yə-bəl 

: incapable of being dissolved in a liquid

also : soluble only with difficulty or to a slight degree