practicality (n.)

early 15c., practicale "of or pertaining to matters of action, practice, or use; applied," with -al (1) + earlier practic (adj.) "dealing with practical matters, applied, not merely theoretical" (early 15c.) or practic (n.) "method, practice, use" (late 14c.).

In some cases directly from Old French practique (adj.) "fit for action," earlier pratique (13c.) and Medieval Latin practicalis, from Late Latin practicus "practical, active," from Greek praktikos "fit for action, fit for business; business-like, practical; active, effective, vigorous," from praktos "done; to be done," verbal adjective of prassein (Attic prattein) "to do, act, effect, accomplish; come to an end, succeed," literally "to pass through, travel," from PIE *per(h)- "go through, cross," an enlargement of the root *per- (2) "to lead, pass over."

Of persons, in reference to skills or occupations, "whose knowledge is derived from practice rather than theory," 1660s. The noun meaning "examination or lesson devoted to practice in a subject" is by 1934. Practical joke "trick played on someone for the sake of annoying him and raising a laugh at his expense" is from 1771 on the notion of "a jest carried into action" (earlier handicraft joke, 1741).

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]