What is the difference between the verbal synonyms "to enhance" and "to improve"? Do they have exactly the same meaning?
Using enhance to mean improve in general and, at the same time, to mean increase, is a serious annoyance to people who care about the words they choose to use. M-W online says it means "heighten, increase; especially : to increase or improve in value, quality, desirability, or attractiveness". Academic writers in all fields, however, have jumped on this buzzword and use it to mean so many things that it has no meaning at all now. It's an academic isomorph of nice.
Dictionary.com has a good example sentence of how to correctly use enhance: "to raise to a higher degree; intensify; magnify: The candlelight enhanced her beauty". She's already beautiful, but in the candlelight, she looks even more beautiful. It doesn't improve or increase her beauty: in the sunlight or the lamplight or the floodlight, she's not more beautiful because she stood in candlelight for a long time. The candlelight didn't actually increase or improve her beauty: if she was a 9 before the candlelight, she'll be a 9 after the candlelight. It merely made her look like a 10 while she was illuminated by candlelight.
Like all synonyms, sometimes they're interchangeable, but sometimes they're not. I've begun to hate the word enhance, so I almost always change it unless it's properly used in context.
In the audit field, we use the term "enhance" when something is in place and generally adequate but it needs a little more to be even better. For example, policies and procedures were in place to manage the risk of rogue trading but it did not say whether it is subject to periodic review and by whom.
We use "improve" when the shortcomings or weaknesses are material and render something inadequate or not up to expectations. Using the same example, the policies and procedures needs improvement because it did not spell out the mechanism to monitor and control trades by traders outside trading hours and off-premise.
To auditors, there is a clear distinction between the two terms.