Definition from Wiktionary, the free dictionary
From French incompatible.
- Of two things: impossible to coexist; not congruous because of differences; irreconcilable; disagreeing.
- (chemistry) Incapable of being together without mutual reaction or decomposition, as certain medicines.
Derived terms 
incompatible (plural incompatibles)
- (medicine, chemistry, chiefly plural) An incompatible substance; one of a group of things that cannot be placed or used together because of a change of chemical composition or opposing medicinal qualities.
- the incompatibles of iron
incompatible (masculine and feminine, plural incompatibles)
incompatible m and f (plural incompatibles)