Insoluble means unable to be dissolved. Insoluble fibre, insoluble in water, an insoluble problem.
Insoluble fibre passes through the gut unchanged and does its work by bulk, where soluble fibre forms a gel — the two do different jobs. Of a problem it means having no solution. Note insolvable, which means the same for problems; and that the Latin means not able to be loosened.
1adjectiveinsolubleUnable to be dissolved.
“Sand is insoluble in water, so it just sinks to the bottom of the glass.”
2adjectivesolutionHaving no solution.
“The problem of how to fit everyone into the tiny flat seemed insoluble.”
Too few real examples of this word to estimate which sense is commonest.
insoluble is a quality of not dissolving.
Latin insolubilis is in- plus solubilis, from solvere, to loosen. Solve and dissolve come from the same loosening.
Proto-Indo-European
*lewh₁-
Latin
insolūbilis
Middle French
insoluble
Middle English
insolible
English, today
insoluble
From Middle English insolible, from Middle French insoluble, from Latin insolūbilis, from in + solūbilis. insolvable. by surface analysis, en + in + soluble.
Etymology from Wiktionary, CC BY-SA