Origin and history of -ing

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. From Middle English it has been much confused with -ing (2), the present-participle adjective suffix, and in modern idiom it can be difficult to say which -ing is meant. This verbal noun suffix -ing (1) is the older; -ing (2) was conformed to it.

suffix used to form the present participles of verbs and the adjectives derived from them, a Middle English alteration or replacement of Old English -end, -ende from PIE *-nt- (source also of Old Frisian -and, Dutch, German -end, Gothic -jands; Sanskrit -ant, Latin -ens, -ans, -antem, Greek -ōn, -ōnt-). Compare -ant.

Present-participles commonly are used as adjectives (living language, which in Old English would be lifende). Those adjectives tend to become nouns of doing (living at home). These meanings veer close to those of English agent-nouns in -ing (among the living). The vowel of -ende weakened in late Old English and the spelling with -g began 13c.-14c. among Anglo-Norman scribes as they naturally merged it formally with the verbal-noun suffix -ing (1).

Old English -ing, patronymic suffix (denoting common origin); surviving in place names (Birmingham, Nottingham) where it denotes "tribe, community."