responsibility n.

"accountable for one's actions, answerable" to another, for an act performed or its consequences, 1640s, from obsolete French responsible (13c., Modern French responsable, as if from Latin *responsabilis), from Latin respons-, past-participle stem of respondere "respond, answer to, promise in return," from re- "back" (see re-) + spondere "to pledge" (see sponsor (n.)).

The meaning "reliable, trustworthy" is from 1690s. It retains the sense of "obligation" in the Latin verb. Related: Responsibly.

With regard to the legal use of the word, two conceptions are often confused — namely, that of the potential condition of being bound to answer or respond in case a wrong should occur, and that of the actual condition of being bound to respond because a wrong has occurred. For the first of these responsible is properly used, and for the second liable. [Century Dictionary]

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]