Etymology
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-in (1)
the adverb in attached to a verb as a word-forming element, by 1960, abstracted from sit-in, which is attested from 1941 in reference to protests and 1937 in reference to labor union actions (which probably was influenced by sit-down strike) but was popularized in reference to civil disobedience protests aimed at segregated lunch counters. As a word-forming element at first of other types of protests, extended by 1965 to any sort of communal gathering (such as love-in, 1967).
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-in (2)
word-forming element in chemistry, usually indicating a neutral substance, antibiotic, vitamin, or hormone; a modification and specialized use of -ine (2).
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-ine (2)
word-forming element in chemistry, often interchangeable with -in (2), though modern use distinguishes them; early 19c., from French -ine, the suffix commonly used to form words for derived substances, hence its extended use in chemistry. It was applied unsystematically at first (as in aniline), but now has more restricted use.

The French suffix is from Latin -ina, fem. form of -inus, suffix used to form adjectives from nouns, and thus is identical with -ine (1).
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-ine (1)
also -in, adjectival word-forming element, Middle English, from Old French -in/-ine, or directly from Latin suffix -inus/-ina/-inum "of, like," forming adjectives and derived nouns, as in divinus, feminus, caninus; from PIE adjectival suffix *-no- (see -en (2)).

The Latin suffix is cognate with Greek -inos/-ine/-inon, and in some modern scientific words the element is from Greek. Added to names, it meant "of or pertaining to, of the nature of" (Florentinus), and so it also was commonly used in forming Roman proper names, originally appellatives (Augustinus, Constantinus, Justinus, etc.) and its descendants in Romanic languages continued active in name-forming. The Latin fem. form, -ina, was used in forming abstracts (doctrina, medicina). Relics of the attempt to continue a distinction between Latin -ina and -inus account for the English hesitation in spelling between -in and -ine.
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-ina 
fem. word- and name-forming element, from Latin -ina (see -ine (1)), or its identical descendants in Spanish, Portuguese, or Italian. The French form is -ine. As a suffix in royal titles (czarina, etc.) it represents an extension from Latin regina.
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-ing (1)
suffix attached to verbs to mean their action, result, product, material, etc., from Old English -ing, also -ung, from Proto-Germanic *-unga-, *-inga- (cognates: Old Norse -ing, Dutch -ing, German -ung). In early use often denoting completed or habitual action; its use has been greatly expanded in Middle and Modern English.
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-ino 
word-ending in some English words from Spanish and Portuguese (albino, casino, etc.), the Spanish and Portuguese form of -ine (1), from Latin -inus/-inum.
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-ing (3)
Old English -ing, patronymic suffix (denoting common origin); surviving in place names (Birmingham, Nottingham) where it denotes "tribe, community."
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-ing (2)

suffix used to form the present participles of verbs and the adjectives derived from them, from Old English present-participle suffix -ende, from PIE *-nt- (cognates: German -end, Gothic -and, Sanskrit -ant, Greek -on, Latin -ans, -ens). The vowel weakened in late Old English and the spelling with -g began 13c.-14c. among Anglo-Norman scribes who naturally confused it with -ing (1).

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-acy 
word-forming element making nouns of quality, state, or condition, a confusion in English of three similar suffixes from Latin: 1. in primacy, etc., from Old French -acie and directly from Medieval Latin -acia, Late Latin -atia, making nouns of quality, state, or condition from nouns in -as. 2. in advocacy, etc., from Late Latin -atia, forming nouns of state from nouns in -atus. 3. in fallacy, etc., from Latin -acia, forming nouns of quality from adjectives in -ax (genitive -acis). Also forming part of -cracy. Extended in English to nouns not found in Latin (accuracy) and to non-Latin words (piracy).
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