darkening

1. gerundparticiplepresentpresent participle and gerund of darken

plural darkenings

1. countableuncountableThe act of something becoming darker.

   NEGATIVE FLASHES — Brief darkenings of a light that is otherwise steadily on.

   1978, Gerald Leonard Howett, Kenneth Low Kelly, E. Thomas Pierce, Emergency vehicle warning lights: state of the art

   1 more example

   At last the first glimpse from a bridge of an open-top red bus, and a noticeable darkening of the atmosphere from the smoke of London: then the increasingly dingy stations with double-barrel names, set amid what has always been to me the outstanding feature of the "Premier Line" approach to London—the positively marvellous display of crazy chimney-pots on the grey inner suburban houses. As many as twenty, all of varying style, standing together like ranks of jagged teeth, and providing a Dickensian back-cloth which no other route can boast.

   1951 October, R. S. McNaught, “Lines of Approach”, in Railway Magazine, page 704