An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1a) A suffix forming the present participle of verbs, e.g. going, observing, writing.
1b) A suffix forming adjectives from participles, e.g. a moving object, a flying bird, a crying baby.
1c) A suffix forming an adjective not derived from a verb, e.g. swashbuckling.
2) A suffix that forms nouns denoting the action of, process of, result of, or something connected with the verb preceding it, e.g. becoming, sleeping, working.

1) M.E. -ing, -inde, from O.E. -ende; cf. Ger. -end, Goth. -and, Gk. -on, L. -ans, Skt. -ant, Av. -ant, Pers. -ân.
2) O.E. -ing, -ung; cf. O.N. -ing, Du. -ing, Ger. -ung.