Etymology
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piety (n.)

mid-14c., piete (late 12c. as a surname), "mercy, tenderness, pity" (senses now obsolete in this word but preserved in its doublet, pity), from Old French piete "piety, faith; pity, compassion" (12c.), from Latin pietatem (nominative pietas) "dutiful conduct, sense of duty; religiousness, piety; loyalty, patriotism; faithfulness to natural ties," in Late Latin "gentleness, kindness, pity;" from pius "kind" (see pious).

From 1570s in English as "filial affection, dutiful conduct or behavior toward one's parents, relatives, country, etc." Meaning "piousness, faith in and reverence for the Supreme Being" is attested in English from c. 1600. Compare pity (n.).

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filial (adj.)
late 14c., from Late Latin filialis "of a son or daughter," from Latin filius "son," filia "daughter," possibly from a suffixed form of PIE root *bheue- "to be, exist, grow" (see be), but Watkins finds it "more likely" assimilated from *felios, originally "a suckling," a suffixed form of PIE root *dhe(i)- "to suck, suckle."
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Pietism (n.)

1690s, in reference to a specific religious movement, Pietism, from German Pietismus, originally applied in derision to the movement to revive personal piety in the Lutheran Church, begun in Frankfurt c. 1670 by Philipp Jakob Spener (1635-1705). See piety + -ism. With lower-case p- and in reference generally to devotion, godliness of life (as distinguished from mere intellectual orthodoxy), by 1829.

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filioque 
Latin, "and from the son," from ablative of filius "son" (see filial). "Clause in Nicene Creed which separates Eastern Church from Western" [Weekley].
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sanctimony (n.)

1530s, "piety, devoutness, sanctity," a sense now obsolete, from French sanctimonie, from Latin sanctimonia "sacredness, holiness, virtuousness," from sanctus "holy" (see saint (n.)). The surviving sense of "external appearance of devoutness, hypocritical or affected piety" is by 1610s.

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Pieta (n.)

"representation in painting or sculpture of the seated Virgin holding the body of of the dead Christ in her lap," 1640s, from Italian pieta, from Latin pietatem "piety, pity, faithfulness to natural ties" (see piety). Earlier in English pity was used in this sense (early 15c.)

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affiliate (v.)
1761, "bring into close association," from Latin affiliatus, past participle of affiliare "to adopt a son," from ad "to" (see ad-) + filius "son" (see filial). Outside legal use, always figurative. Related: Affiliated; affiliating.
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filicide (n.)
1660s, "action of killing a son or daughter," from Latin filius/filia "son/daughter" (see filial) + -cide "a killing." Meaning "one who kills a son or daughter" is from 1823. Related: Filicidal.
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fitz (n.)
Anglo-French fitz, from Old French fils, from Latin filius "son of" (see filial); used regularly in official rolls and hence the first element of many modern surnames; in later times used of illegitimate issue of royalty.
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affiliation (n.)

1751, "adoption," from French affiliation, from Medieval Latin affiliationem (nominative affiliatio), noun of action from past-participle stem of Latin affiliare "to adopt as a son," from ad "to" (see ad-) + filius "son" (see filial). Figurative sense of "adoption by a society, of branches" first recorded 1799 (the verb affiliate in a related sense is from 1761). Meaning "friendship, relationship, association" is from 1852.

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