"set apart and consecrated to a deity or to a sacred purpose by a solemn act or by religious ceremonies; devoted with earnest purpose, as to some person or end," c. 1600, usually of things, writings, property, etc., past-participle adjective from dedicate (v.).

Of persons, "devoted to one's aims or vocation," attested clearly by 1936, but the sense shift can be felt in Lincoln's Gettysburg Address, which opens talking of "a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal," and a few lines later reintroduces the word personally: "It is for us, the living, rather, to be dedicated here to the unfinished work which they who fought here, have, thus far, so nobly advanced. It is rather for us to be here dedicated to the great task remaining before us ...."

Of things, "made to be available only for a particular purpose or class of user," by 1969. Related: Dedicatedly. 

1540s, "a word," a sense now obsolete, from Late Latin dictionem (nominative dictio) "a saying, expression; a word; kind of delivery, style," noun of action from past-participle stem of Latin dicere "to say, state, proclaim, make known, allege, declare positively" (source of French dire "to say"), which is related to dicare "to talk, speak, utter, make speech; pronounce, articulate," both from PIE root *deik- "to show," also "pronounce solemnly." The meaning "manner of saying," especially in reference to the choice of words, is from 1700.

Latin dicere and dicare are presumed to have been originally the same word. De Vann writes that "the verb dicāre may well have been backformed from compounds in -dicāre." The basic sense in both is "to talk, speak, declare." They seem to have divided, imperfectly, the secondary senses between them: dicere "to say, state, proclaim, make known, allege, declare positively; plead (a case);" in religion, "to dedicate, consecrate," hence, transferred from the religion sense, "give up, set apart, appropriate;" dicare "to talk, speak, utter, make speech; pronounce, articulate; to mean, intend; describe; to call, to name; appoint, set apart."

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

Proto-Indo-European root meaning "to show," also "pronounce solemnly," "also in derivatives referring to the directing of words or objects" [Watkins].

It might form all or part of: abdicate; abdication; addict; adjudge; apodictic; avenge; benediction; betoken; condition; contradict; contradiction; dedicate; deictic; deixis; dictate; diction; dictionary; dictum; digit; disk; ditto; ditty; edict; Eurydice; index; indicate; indication; indict; indiction; indictive; indite; interdict; judge; judicial; juridical; jurisdiction; malediction; malison; paradigm; policy (n.2) "written insurance agreement;" preach; predicament; predicate; predict; prejudice; revenge; soi-disant; syndic; teach; tetchy; theodicy; toe; token; valediction; vendetta; verdict; veridical; vindicate; vindication; voir dire.

It might also be the source of: Sanskrit dic- "point out, show;" Greek deiknynai "to show, to prove," dikē "custom, usage;" Latin dicere "speak, tell, say," digitus "finger," Old High German zeigon, German zeigen "to show," Old English teon "to accuse," tæcan "to teach."