Origin and history of liability

mid-15c., "bound or obliged by law," from Old French lier, liier "to bind, tie up, fasten, tether; bind by obligation" (12c.), from Latin ligare "to bind, to tie" (from PIE root *leig- "to tie, bind"). With -able.

Perhaps it is from an Anglo-French *liable, or from an unattested word in Old French or Medieval Latin. The general sense of "exposed to" (something undesirable) is attested by 1590s. The unetymological use for "likely" is attested by 1850.

word-forming element making abstract nouns from adjectives and meaning "condition or quality of being ______," from Middle English -ite, from Old French -ete (Modern French -ité) and directly from Latin -itatem (nominative -itas), suffix denoting state or condition, composed of -i- (from the stem or else a connective) + the common abstract suffix -tas (see -ty (2)).

Roughly, the word in -ity usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances; & the word in -ism means the disposition, or collectively all those who feel it. [Fowler]