Etymology
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conjugal (adj.)

1540s, "pertaining to marriage, nuptial," also "pertaining to the relationship of husband and wife," from French conjugal (13c.), from Latin coniugalis "relating to marriage," from coniunx (genitive coniugis) "spouse," which is related to coniugare "to join together," from assimilated form of com "with, together" (see con-) + iugare "to join," from iugum "yoke" (from PIE root *yeug- "to join"). Related: Conjugacy; conjugality.

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courtship (n.)

1570s, "behavior of a courtier," from court (n.) + -ship. Meaning "the wooing of a woman, attention paid by a man to a woman with intention of winning her affection and ultimately her consent to marriage" is from 1590s. By 1830s it was used of a period during which a couple mutually develops a romantic relationship with a view to marriage.

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parentage (n.)

late 15c., "parental conduct, parental relationship exhibited in the recognition and care of children," from Old French parentage (12c.), from parent (see parent (n.)). Meaning "descent or derivation from parents, lineage" is from 1560s; figurative use from 1580s. An earlier word was parage "descent, lineage; family," late 13c., from Old French.

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*ghos-ti- 

Proto-Indo-European root meaning "stranger, guest, host," properly "someone with whom one has reciprocal duties of hospitality," representing "a mutual exchange relationship highly important to ancient Indo-European society" [Watkins]. But as strangers are potential enemies as well as guests, the word has a forked path.

The word ghos-ti- was thus the central expression of the guest-host relationship, a mutual exchange relationship highly important to ancient Indo-European society. A guest-friendship was a bond of trust between two people that was accompanied by ritualized gift-giving and created an obligation of mutual hospitality and friendship that, once established, could continue in perpetuity and be renewed years later by the same parties or their descendants. [Calvert Watkins, "American Heritage Dictionary of Indo-European Roots"]

It forms all or part of: Euxine; guest; hospice; hospitable; hospital; hospitality; hospodar; host (n.1) "person who receives guests;" host (n.2) "multitude;" hostage; hostel; hostile; hostility; hostler; hotel; Xenia; xeno-; xenon.

It is the hypothetical source of/evidence for its existence is provided by: Greek xenos "guest, host, stranger;" Latin hostis, in earlier use "a stranger," in classical use "an enemy," hospes "host;" Old Church Slavonic gosti "guest, friend," gospodi "lord, master;" Old English gæst, "chance comer, a stranger."

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gentility (n.)
mid-14c., "nobility of birth, gentle birth," from Old French gentilité (14c.), from Latin gentilitatem (nominative gentilitas) "relationship in the same family or clan," from gentilis "of the same family or clan" (see gentle; also compare gentry). From 1640s as "social superiority." Meaning "state of being gentile" is rare.
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naturalism (n.)

1630s, "action based on natural instincts," from natural (adj.) + -ism. In philosophy, as a view of the world and humanity's relationship to it involving natural forces only (and excluding spiritualism and superstition), from 1750. As a tendency in art and literature, "conformity to nature or reality, but without slavish fidelity to it," from 1850.

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in-law (n.)

1894, "anyone of a relationship not natural," abstracted from father-in-law, etc.

The position of the 'in-laws' (a happy phrase which is attributed ... to her Majesty, than whom no one can be better acquainted with the article) is often not very apt to promote happiness. [Blackwood's Magazine, 1894]

The earliest recorded use of the formation is in brother-in-law (13c.); the law is Canon Law, which defines degrees of relationship within which marriage is prohibited. Thus the word originally had a more narrow application; its general extension to more distant relatives of one's spouse is, according to OED "recent colloquial or journalistic phraseology." Middle English inlaue (13c.) meant "one within or restored to the protection and benefit of the law" (opposite of an outlaw), from a verb inlauen, from Old English inlagian "reverse sentence of outlawry."

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mood (n.2)

"grammatical form indicating the function of a verb," 1570s, an alteration of mode (n.1). The grammatical and musical (1590s) usages of it influenced the meaning of mood (n.1) in such phrases as light-hearted mood, but it is worth remembering that the two moods have no etymological relationship. Also used in traditional logic (1560s) as a variant of mode.

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ecology (n.)
Origin and meaning of ecology

1873, oecology, "branch of science dealing with the relationship of living things to their environments," coined in German by German zoologist Ernst Haeckel as Ökologie, from Greek oikos "house, dwelling place, habitation" (from PIE root *weik- (1) "clan") + -logia "study of" (see -logy). In use with reference to anti-pollution activities from 1960s.

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liege (n.)
late 14c., "vassal of a feudal lord," also "a feudal sovereign, a liege-lord," probably from liege (adj.)) or from a noun use of the adjective in Old French or Anglo-French. A fully reciprocal relationship, so the adjective could apply to either party. Old French distinguished them as lige seignur "liege-lord" and home lige "liege-man."
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