The crossword solution for the term 'Onset of Evening' is 'LONGE', which is a five-letter word. Longe is a type of rope used to tether a horse, usually attached to the horse's halter or bridle and then to a post or hitching rail. It is also used to help train horses by allowing them to move in a circle while the trainer stands in the center. The term 'longe' is derived from the French word 'LONGER', meaning 'to lengthen'.