improver

Etymology 1

improve + -er

noun

1. Something that, or someone who, improves something.
   He introduced and encouraged manufactures of all kinds; and no inventor or improver of any ingenious art did he suffer to go unrewarded. 1754, David Hume, chapter 2, in The History of England, from the Invasion of Julius Cæsar to the Revolution in 1688, volume I, London: T. Cadell, published 1770, page 105
   Never did Christmas board display a more goodly and gracious assemblage of countenances: those who were not handsome were, at least, happy; and happiness is a rare improver of your hard-favoured visage. 1876, Washington Irving, “The Christmas Dinner”, in Old Christmas, London: Macmillan, page 123
   What a song. What an instant mood improver. It’ll make you forget all the tension you had built up […] 16 December 2015, Mitch Feltscheer, “9 best musical duos of all time according to Us The Band”, in Music Feed
2. (obsolete) Specifically, a person who improves land or property, a landscaper.
   […] may not one say Homer is in this like a skilful Improver, who places a beautiful Statue in a well-disposed Garden so as to answer several Vistas, and by that Artifice one single Figure seems multiply’d into as many Objects as there are Openings from whence it may be viewed? 1716, Alexander Pope, “An Essay on Homer’s Battels”, in The Iliad of Homer, volume II, London: Bernard Lintot, page 4
3. One who improves his or her performance, one who shows improvement (of individuals or groups).
   The hotel can also arrange beginner and improver angling lessons with a local instructor. 27 August 2011, “Stay the Night: The Blackaddie Hotel, Sanquhar”, in The Independent
   The biggest improvers over the last year, according to the index were Côte d’Ivoire, Egypt, Saint Vincent and the Grenadines […] 3 December 2014, Charlie Taylor, “Ireland improves to 17 out of 175 countries on corruption index”, in The Irish Times
   The last-named player was given outings in three of the four Tests against England recently, and although plenty of rough edges remained understandably apparent, he gave the impression of being a willing learner and improver. 28 January 2016, Rob Houwing, “Piedt making quiet SA strides”, in Sport24
4. A substance added to cause improvement (especially to a foodstuff).
   Soy flour is often added to bread as an improver. It helps the dough texture and can make the bread quite soft. 6 August 2016, Wendyl Nissen, “Who kneads so many ingredients?”, in The New Zealand Herald
   When planting a new olive tree, mix organic soil improver and fertiliser into the planting hole and keep the soil moist while the olive establishes itself. 7 February 2017, “Gardening: Get a taste of the Mediterranean”, in The Northern Star
5. (historical) A pad worn by women to make the dress hang properly.

Etymology 2

improv + -er

noun

1. One who performs improv; a improviser.