Etymology
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-escent 
word-forming element meaning "beginning, becoming, tending to be," from Latin -escentem (nominative -escens), ending of present participles of verbs in -escere.
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-faction 
word-forming element making nouns of action from verbs, from Latin -factionem (nominative -factio), from facere "to make" (from PIE root *dhe- "to set, put").
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-osity 
word-forming element making nouns from adjectives in -ous, -ose (1); from French -osité, from Latin -ositatem (nominative -ositas), properly -ose + -ity.
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-ion 
word-forming element attached to verbs, making nouns of state, condition, or action, from French -ion or directly from Latin -ionem (nominative -io, genitive -ionis), common suffix forming abstract nouns from verbs.
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-a (2)
nominative neuter plural ending of certain nouns and adjectives in Latin and Greek that have been adopted into English (phenomena, data, media, criteria, etc.). It also is common in biology in Modern Latin formations of class names (Mammalia, Reptilia, Crustacea).
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-ty (2)
suffix used in forming abstract nouns from adjectives (such as safety, surety), Middle English -tie, -te, from Old French -te (Modern French -té), from Latin -tatem (nominative -tas, genitive -tatis), cognate with Greek -tes, Sanskrit -tati-. Also see -ity.
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-acious 
compound adjectival word-forming element of Latin origin, attached to verb stems and expressing intensity of action: "given to, inclined to, abounding in," or expressing intensity of physical or mental action, from Latin -aci- (nominative -ax, accusative -acem), noun ending used with verbal stems (see -acea), + -ous. The accompanying nouns are formed in -acity.
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-ent 

word-forming element making adjectives from nouns or verbs, from French -ent and directly from Latin -entem (nominative -ens), present-participle ending of verbs in -ere/-ire. Old French changed it in many words to -ant, but after c. 1500 some of these in English were changed back to what was supposed to be correct Latin. See -ant.

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-s (1)

suffix forming almost all Modern English plural forms of nouns, gradually extended in Middle English as -es from Old English -as, the nominative plural and accusative plural ending of certain "strong" masculine nouns (such as dæg "day," nominative/accusative plural dagas "days"). The commonest Germanic declension, traceable back to the original PIE inflection system, it is also the source of the Dutch -s plurals and (by rhotacism) Scandinavian -r plurals (such as Swedish dagar).

Much more uniform today than originally; Old English also had a numerous category of "weak" nouns that formed their plurals in -an, and other strong nouns that formed plurals with -u. Quirk and Wrenn, in their Old English grammar, estimate that 45 percent of the nouns a student will encounter will be masculine, nearly four-fifths of them with genitive singular -es and nominative/accusative plural in -as. Less than half, but still the largest chunk.

The triumphs of -'s possessives and -s plurals represent common patterns in language: using only a handful of suffixes to do many jobs (such as -ing), and the most common variant squeezing out the competition. To further muddy the waters, it's been extended in slang since 1936 to singulars (such as ducks,sweets,babes) as an affectionate or diminutive suffix.

Old English single-syllable collectives (sheep, folk) as well as weights, measures, and units of time did not use -s. The use of it in these cases began in Middle English, but the older custom is preserved in many traditional dialects (ten pound of butter; more than seven year ago; etc.).

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-ae 
occasional plural suffix of words ending in -a (see a- (1)), most of which, in English, are from Latin nominative fem. singular nouns (or Greek ones brought up through Latin), which in Latin form their plurals in -ae. But plurals in native -s were established early in English for many of them (such as idea, arena) and many have crossed over since. Now it is not possible to insist on purity one way or the other without breeding monsters.
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