Etymology
Advertisement
-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).
Related entries & more 
Advertisement
-in (2)
word-forming element in chemistry, usually indicating a neutral substance, antibiotic, vitamin, or hormone; a modification and specialized use of -ine (2).
Related entries & more 
-ado 
in commando, desperado, tornado, and other words of Spanish and Portuguese origin, "person or group participating in an action," from Latin -atus, past participle suffix of verbs of the first conjugation (see -ade).
Related entries & more 
-al (3)
word-forming element in chemistry to indicate "presence of an aldehyde group" (from aldehyde). The suffix also is commonly used in forming the names of drugs, often narcotics (such as barbital), a tendency that apparently began in German and might have been suggested by chloral (n.).
Related entries & more 
-some (2)
suffix added to numerals meaning "a group of (that number)," as in twosome, from pronoun use of Old English sum "some" (see some). Originally a separate word used with the genitive plural (as in sixa sum "six-some"); the inflection disappeared in Middle English and the pronoun was absorbed. Use of some with a number meaning "approximately" also was in Old English.
Related entries & more 
Advertisement
-id 
adjectival word-forming element, especially in zoology, "belonging to, connected with, member of a group or class," in some cases probably via from French -ide, back-formed from Modern Latin names of zoological classes in -idae, as arachnid "a spider" from the biological class name arachnidae.

This -idae is the plural of Latin -ides, a masculine patronymic (indicating "descent from"), from Greek -ides "son of," denoting descent from the person to whose name it is attached (such as Heraklides).

In astronomy, of meteor showers, "having its radiant in" the constellation named (Perseid, Leonid, etc.), it probably represents Latin -idis, from Greek -idos, the genitive of the feminine form of the patronymic suffix.
Related entries & more 
-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).
Related entries & more 
-farious 

word-forming element, from Latin -farius, -fariam "in (so many) parts," as in bifariam "in two parts or places, in two ways;" multifariam "in many places," an element of disputed origin. Watkins suggests it is from PIE *dwi-dhe- "making two," from roots *dwi- "two" + *dhe- "to put, set." It also has been derived from Latin fari "to say" (as in nefarious), but de Vaan writes that "the alleged semantic development to 'in n ways' is obscure," and he points to the suggestion of a PIE *-dho-, with cognates in Sanskrit dvidha (adv.) "twofold;" tridha "threefold."

Related entries & more 
-ia 
word-forming element in names of countries, diseases, and flowers, from Latin and Greek -ia, noun ending, in Greek especially used in forming abstract nouns (typically of feminine gender); see -a (1). The classical suffix in its usual evolution (via French -ie) comes to Modern English as -y (as in familia/family, also -logy, -graphy). Compare -cy.

In paraphernalia, Mammalia, regalia, etc. it represents Latin or Greek -a (see -a (2)), plural suffix of nouns in -ium (Latin) or -ion (Greek), with formative or euphonic -i-.
Related entries & more 
-y (3)
suffix in pet proper names (such as Johnny, Kitty), first recorded in Scottish c. 1400; according to OED it became frequent in English 15c.-16c. Extension to surnames seems to date from c. 1940. Use with common nouns seems to have begun in Scottish with laddie (1546) and become popular in English due to Burns' poems, but the same formation appears to be represented much earlier in baby and puppy.
Related entries & more