a suffix, occurring in adjectives of Greek and Latin origin, meaning “pertaining to,” and (in nouns thence derived) also imitated in English (coffin; cousin , etc.).

Middle English -in, -ine < Old French < Latin -inus, -ina, -inum < Greek -inos, -inē, -inon

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a noun suffix used in a special manner in chemical and mineralogical nomenclature (glycerin; acetin , etc.). In spelling, usage wavers between -in and -ine. In chemistry a certain distinction of use is attempted, basic substances having the termination -ine rather than -in (aconitine; aniline , etc.), and -in being restricted to certain neutral compounds, glycerides, glucosides, and proteids (albumin; palmitin , etc.), but this distinction is not always observed.

< Neo-Latin -ina. See -ine2


a suffixal use of the adverb in, extracted from sit-in, forming compound nouns, usually from verbs, referring to organized protests through or in support of the named activity (kneel-in; chain-in; be-in ) or, more generally, to any organized social or cultural activity (cook-in; sing-in ).
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World English Dictionary
suffix forming nouns
1.  indicating a neutral organic compound, including proteins, glucosides, and glycerides: insulin; digitoxin; tripalmitin
2.  indicating an enzyme in certain nonsystematic names: pepsin
3.  indicating a pharmaceutical substance: penicillin; riboflavin; aspirin
4.  indicating a chemical substance in certain nonsystematic names: coumarin
[from New Latin -ina; compare -ine²]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

suffix attached to a verb originated 1960 with sit-in (which was probably influenced by sit-down strike), used first of protests, extended c.1965 to any gathering.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

-in suff.

  1. Neutral chemical compound: inulin.

  2. Pharmaceutical: rifampin.

  3. Antibiotic: penicillin.

  4. Antigen: tuberculin.

  5. Variant of -ine2.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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