The gerundive adjective is grieving.

It is the gerundive form of "to happen".

No, "running" is not a gerundive. A gerundive is a verbal adjective formed from a verb in Latin that expresses necessity or obligation, whereas "running" functions as a gerund in English, which is a verbal noun that can act as a subject, object, or complement in a sentence.

No. Playing is the gerundive form of the verb to play.

L. Graham H. Horton-Smith has written:

'Furthe notes on the origin of the gerund and gerundive' -- subject(s): Gerund, Gerundive, Latin language

'On a wreath for a friend of college days, Percy W.G. Sargent, victim for the nonce of a very pun-y pun!'

'Ars Tragica Sophoclea cum Shaksperiana comparata' -- subject(s): Tragedies

'Rhyming relics of the legal past'

'The Italic verb eehiia- ehia-' -- subject(s): Italic languages and dialects

'Concluding notes on the origin of the gerund and gerundive' -- subject(s): Gerund, Gerundive, Latin language

'Notes on Rigveda I. 48. 15' -- subject(s): Vedas