Etymology
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affinity (n.)
c. 1300, "relation by marriage" (as opposed to consanguinity), from Old French afinite "relationship, kinship; neighborhood, vicinity" (12c., Modern French affinité), from Latin affinitatem (nominative affinitas) "relationship by marriage; neighborhood," noun of state from affinis "adjoining, adjacent," also "kin by marriage," literally "bordering on," from ad "to" (see ad-) + finis "a border, a boundary" (see finish (v.)).

Spelling was re-Latinized in early Modern English. Used figuratively in English since c. 1600 of structural relationships in chemistry, philology, geometry, etc. Meaning "natural liking or attraction, a relationship as close as family between persons not related by blood" is from 1610s.
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paraffin (n.)

colorless, tasteless fatty crystalline substance obtained from petroleum, etc., 1838, from German Paraffin, coined c. 1830 by German chemist Karl von Reichenbach (1788-1869), who first obtained it as a waxy substance from wood tar, irregularly from Latin parum "not very, too little," which probably is related to parvus "little, small" (from PIE root *pau- (1) "few, little") + affinis "associated with" (see affinity). So called because paraffin is chemically not closely related to other substances. The liquid form (originally paraffin oil) Reichenbach called eupion, but this was the standard meaning of paraffin in English by 1860.

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relationship (n.)

1640s, "sense or state of being related" by kindred, affinity, or other alliance, from relation + -ship. Specifically of romantic or sexual intimacy by 1944.

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congeniality (n.)

1610s, "state of being kindred; affinity of character or interests;" as if from Latin but apparently a modern formation; compare congenial + -ity.

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petunia (n.)

genus of ornamental plants native to South America and Mexico, 1825, from Modern Latin Petunia (1789), from French petun (16c.), an obsolete word for "tobacco plant" (in Century Dictionary, 1890, "said to be still in use in some parts of Canada"), from Portuguese petum, evidently from Guarani (Paraguay) pety. The petunia has a botanical affinity to the tobacco plant. See tobacco.

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congenial (adj.)

1620s, "kindred, partaking of the same nature or natural characteristics," from assimilated form of Latin com "with, together" (see con-) + genialis "of birth," thus, "kindred" (from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups). Sense of "agreeable" is first recorded 1711 on the notion of "having natural affinity." Also compare congenital.

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chromatin (n.)

protoplasm in cell nuclei, 1882, from German, coined 1879 by German anatomist Walther Flemming (1843-1905), from Latinized form of Greek khrōmat-, the correct combinational form of khrōma "color" (see chroma) + chemical suffix -in (2). So called because it has a special affinity for coloring matter and stains readily. Related: Chromatid. Compare chromosome.

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sagebrush (n.)

collective name for a type of dry, shrubby plant that grows over the vast dry plains of the western U.S., by 1846, from sage (n.1), to which it has no biological affinity, + brush (n.2). Said to be so called for resemblance of its appearance or odor.

Sage-brush is very fair fuel, but as a vegetable it is a distinguished failure. Nothing can abide the taste of it but the jackass and his illegitimate child, the mule. ["Mark Twain," "Roughing It"]
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chemistry (n.)

c. 1600, "alchemy," from chemist + -ry; also see chemical (adj.). The meaning "natural physical process" is from 1640s; the sense of "scientific study of the composition of material things and the changes they undergo" is by 1788. Chemistry in the European mind disengaged itself from alchemy in the mid-1600s; The Academy del Cimento was established in Italy in 1657, the Royal Society in London in 1660, and the Academy of Sciences in Paris in 1666.

The figurative sense of "instinctual attraction or affinity" is attested slightly earlier, from the alchemical sense.

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sympathy (n.)
Origin and meaning of sympathy

1570s, "affinity between certain things," from French sympathie (16c.) and directly from Late Latin sympathia "community of feeling, sympathy," from Greek sympatheia "fellow-feeling, community of feeling," from sympathes "having a fellow feeling, affected by like feelings," from assimilated form of syn- "together" (see syn-) + pathos "feeling" (from PIE root *kwent(h)- "to suffer").

In English, almost a magical notion at first; used in reference to medicines that heal wounds when applied to a cloth stained with blood from the wound. Meaning "conformity of feelings" is from 1590s; sense of "fellow feeling, compassion" is first attested c. 1600. An Old English loan-translation of sympathy was efensargung.

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