1640s, as a theological term (in reference to "covenants" between God and man), from French fédéral, an adjective formed from Latin foedus (genitive foederis) "covenant, league, treaty, alliance" (from PIE *bhoid-es-, suffixed form of root *bheidh- "to trust, confide, persuade").
Secular meaning "pertaining to a covenant or treaty" (1650s) led to political sense of "formed by agreement among independent states" (1707), from use of the word in federal union "union based on a treaty" (popularized during formation of U.S.A. 1776-1787) and like phrases. Also from this period in U.S. history comes the sense "favoring the central government" (1788) and the especial use of the word (as opposed to confederate) to mean a state in which the federal authority is independent of the component parts within its legitimate sphere of action. Used from 1861 in reference to the Northern forces in the American Civil War.
mid-15c., "adherent of a religion opposed to Christianity," from Old French infidèle, from Latin infidelis "unfaithful, not to be trusted," in Late Latin "unbelieving" (in Medieval Latin also as a noun, "unbeliever"), from in- "not, opposite of" (see in- (1)) + fidelis "faithful" (from PIE root *bheidh- "to trust, confide, persuade").
Originally "a non-Christian" (especially a Saracen); later "one who does not believe in religion, disbeliever in religion generally" (1520s). Also used to translate Arabic qafir (see Kaffir), which is from a root meaning "to disbelieve, to deny," strictly referring to all non-Muslims but virtually synonymous with "Christian;" hence, from a Muslim or Jewish point of view, "a Christian" (1530s). As an adjective from mid-15c., "of a religion opposed to Christianity;" 1520s as "rejecting the Christian religion while accepting no other."
late 14c., "contract between two or more persons, states, etc., for mutual support or joint action," from Anglo-French confederacie (Old French confederacie), from stem of Latin confoederare "to unite by a league," from assimilated form of com "with, together" (see con-) + foederare, from foedus "a league" (from suffixed form of PIE root *bheidh- "to trust, confide, persuade").
Also late 14c. as "an aggregation of persons, states, etc., united by a league, a confederation. At first in reference to leagues of classical Greek states (Aetolian, Delian, Achaean, etc.), later of the Netherlands. In 17c.-18c. often in a bad sense, especially "a conspiracy against a superior."
The word was used of the United States of America under (and in) the Articles of Confederation (1777-1788). In reference to the national organization of the seceding Southern states (1861-1865, also Southern Confederacy) from 1861, in the constitution of the Confederate States of America, formed by constitutional convention at Montgomery, Alabama, March 11, 1861.
Confederacy now usually implies a looser or more temporary association than confederation, which is applied to a union of states organized on an intentionally permanent basis. [OED]
mid-13c., faith, feith, fei, fai "faithfulness to a trust or promise; loyalty to a person; honesty, truthfulness," from Anglo-French and Old French feid, foi "faith, belief, trust, confidence; pledge" (11c.), from Latin fides "trust, faith, confidence, reliance, credence, belief," from root of fidere "to trust,"from PIE root *bheidh- "to trust, confide, persuade." For sense evolution, see belief. Accommodated to other English abstract nouns in -th (truth, health, etc.).
From early 14c. as "assent of the mind to the truth of a statement for which there is incomplete evidence," especially "belief in religious matters" (matched with hope and charity). Since mid-14c. in reference to the Christian church or religion; from late 14c. in reference to any religious persuasion.
And faith is neither the submission of the reason, nor is it the acceptance, simply and absolutely upon testimony, of what reason cannot reach. Faith is: the being able to cleave to a power of goodness appealing to our higher and real self, not to our lower and apparent self. [Matthew Arnold, "Literature & Dogma," 1873]
From late 14c. as "confidence in a person or thing with reference to truthfulness or reliability," also "fidelity of one spouse to another." Also in Middle English "a sworn oath," hence its frequent use in Middle English oaths and asseverations (par ma fay, mid-13c.; bi my fay, c. 1300).