improver

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.”

   “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.”

   “What a song. What an instant mood improver. It’ll make you forget all the tension you had built up […]”

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?”

   “He had been visiting a friend in a neighbouring county, and that friend having recently had his grounds laid out by an improver, Mr. Rushworth was returned with his head full of the subject, and very eager to be improving his own place in the same way; […]”

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.”

   “The biggest improvers over the last year, according to the index were Côte d’Ivoire, Egypt, Saint Vincent and the Grenadines […]”

   “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.”

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.”

   “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.”

5. (historical)A pad worn by women to make the dress hang properly.
6. One who performs improv; an improviser.