These words mean to bring something to a higher level of quality, efficiency, etc. Improve is the most general word in this group; it can mean to increase, enlarge, correct or raise, as in the following examples: to improve one’s vocabulary; to improve one’s understanding of world affairs; to improve one’s habits; to improve one’s marks in school. Improve thus refers to any means of making something higher in quality or more desirable nature.

Better , more colloquial in tone, is in some contexts interchangeable with improve : to better (or improve ) one’s marks. But as a rule it has more narrow implication, often suggesting only a modest increase or elevation in knowledge or appreciation. Although improve can also be used to describe such situations, in contexts implying a profound or important elevation of status or quality, improve is more likely to be used: Through keen management procedures and a substantial investment the company’s market potential was vastly improved . Better is often used reflexively with the sense of improving socially or economically.

• He took the new job to better himself; He cultivated socialites in the hope of bettering himself.

Better so used often has a distinctly vulgar tone. The greater scope and importance that attaches to improve is immediately evident if one contrasts to improve oneself with to better oneself : He went to night school to improve himself .

Ameliorate is usually applied to conditions rather than to specific things, and suggests that the conditions are much in need of correction: The city council considered framing new ordinances to ameliorate the unsanitary conditions and slum areas. Meliorate has the same meaning as ameliorate , but is nowadays less often used. Both words, but especially meliorate , are extremely formal or literary: missionaries whose aim was to meliorate the ignorance of the indigenous peoples.