1Australian, New Zealand informal The action or habit of arriving at a sheep station, farm, etc., in the evening under the pretence of seeking work, so as to obtain food and shelter; the way of life of a sundowner. Now chiefly historical.
2North American A marked increase in symptoms, such as confusion, disorientation, agitation, etc., towards the end of the day or during the night in a person suffering from dementia, typically Alzheimer's in the middle stages.
Late 19th century; earliest use found in Melbourne Punch. From sundown + -ing, after sundowner.