suffix expressing ability or capacity, from L. -abilitas, forming nouns from adjs. ending in -abilis (see able). Not etymologically related to ability, though popularly connected with it.
suffix expressing ability, capacity, fitness, from L. -ibilis, -abilis, forming adjectives from verbs, from PIE *tro-, a suffix used to form nouns of instrument. In L., infinitives in -are took -abilis, others -ibilis; in Eng., able is used for native words, -ible for words of obvious L. origin.