c. 1500, "a ceasing, an ending; a going away, act of leaving" (obsolete in this sense), from Old French departement "division, sharing out; divorce, parting" (12c.), from Late Latin departire "to divide" (transitive), from de- "from" (see de-) + partire "to part, divide," from pars (genitive partis) "a part, piece, a share, a division" (from PIE root *pere- (2) "to grant, allot").

French department came also to mean "group of people" (as well as "departure"), and from this by 1735 English had borrowed the sense of "separate division of a complex whole, separate business assigned to someone in a larger organization, distinct branch or group of activities" (science, business, manufacture, the military). The specific meaning "separate division of a government" is from 1769. As an administrative district in France, from 1792.

Department store "store that sells a variety of items, organized by department" is from 1878.

The "Department Store" is the outgrowth of the cheap counter business originated by Butler Brothers in Boston about ten years ago. The little "Five Cent Counter" then became a cornerstone from which the largest of all the world's branches of merchandising was to be reared. It was the "Cheap Counter" which proved to the progressive merchant his ability to sell all lines of wares under one roof. It was the Five Cent Counter "epidemic" of '77 and '78 which rushed like a mighty whirlwind from the Atlantic to the Pacific and all along its path transformed old time one line storekeepers into the wide-awake merchant princes of the present day. It was this same epidemic which made possible the world famed Department Stores of Houghton, of Boston; Macy, of New York; Wanamaker, of Philadelphia; and Lehman, of Chicago. [American Storekeeper, 1885] 

mid-12c., "the exercise of authority in vindication of right by assigning reward or punishment;" also "quality of being fair and just; moral soundness and conformity to truth," from Old French justice "justice, legal rights, jurisdiction" (11c.), from Latin iustitia "righteousness, equity," from iustus "upright, just" (see just (adj.)).

Justice is the end of government. It is the end of civil society. It ever has been and ever will be pursued until it be obtained, or until liberty be lost in the pursuit. ["The Federalist," No. 51]

Meaning "right order, equity, the rewarding to everyone of that which is his due" in English is from late 14c. The Old French word had widespread senses including also "uprightness, equity, vindication of right, court of justice, judge." To the Greek philosophers (Plato, Aristotle) the notion was of each thing in its proper sphere or serving its proper purpose; inequality of aptitudes and outcomes was implied.

In English c. 1400-1700 sometimes also with a vindictive sense "infliction of punishment, legal vengeance." As a title for a judicial officer, c. 1200. Justice of the peace is attested from early 14c. To do justice to (someone or something) "deal with as is right or fitting" is from 1670s. In the Mercian hymns, Latin iustitia is glossed by Old English rehtwisnisse.

late 14c., "of or pertaining to a judge; pertaining to the administration of justice," from Latin iudicialis "of or belonging to a court of justice," from iudicium "judgment, decision of a court of justice," also the court itself, from iudex "a judge," a compound of ius "right, law" (see just (adj.)) + root of dicere "to say" (from PIE root *deik- "to show," also "pronounce solemnly"). Related: Judicially.

abbreviation of department, attested from 1869.

"amenable to law, subject to judicial trial," mid-15c., from Anglo-French and Old French justiciable "pertaining to justice or law," hence "proper to be brought before a court of justice," from justicier, from Latin iustitia "righteousness; equity" (see justice).

Persian masc. proper name, in classical history a son of Xerxes II, also a son of Darius, from Greek Artaxerxes, from Old Persian Artaxšaca, literally "having a kingdom of justice," from arta- "justice" + xšaca "kingdom."

"administrator of justice," 1540s; later as an adjective, "pertaining to the law" (1580s), from Medieval Latin justiciarius, from Latin iustitia (see justice (n.)).

1791, "pertaining to a (French) department, pertaining to a division of a country," from French départmental, from département (see department). Meaning "of departmental systems generally" from 1832. Related: Departmentally.

1939, from abbreviation of Military Intelligence, followed by the department number.

"vindication of divine justice," 1771, from French théodicée, title of a 1710 work by Leibniz to prove the justice of God in a world with much moral and physical evil, from Greek theos "god" (from PIE root *dhes-, forming words for religious concepts) + dike "custom, usage; justice, right; court case" (see Eurydice). Related: Theodicean.