noun, noun which may take the genitive case particle 'no'
impromptu; spontaneous creation
Literary term for something created on the spur of the moment, especially a poem or piece of writing. Often used in titles or descriptions of artistic works.
この詩は散歩中に偶成したものです。
This poem was composed impromptu during a walk.
彼の偶成の句が新聞に載った。
His impromptu haiku appeared in the newspaper.