a combination of -able and -ity, found on nouns corresponding to adjectives in -able: capability.

Origin of -ability

Middle English -abiliteLatin -ābilitās
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Word Origin and History for -ability

word-forming element expressing ability, fitness, or capacity, from Latin -abilitas, forming nouns from adjectives ending in -abilis (see -able). Not etymologically related to ability, though popularly connected with it.

Online Etymology Dictionary, © 2010 Douglas Harper