How do I use the prefix 'de-' correctly?

Is there a dictionary dedicated to word prefixes? I'd like to know more about de-, but there's no uniform meaning; for example, in demystify it signifies a reverse action, while in delimit it's a positive meaning, like set.

Solution 1:

I don't think there is a dictionary dedicated solely to prefixes. But you can find some common prefixes and their definitions in normal dictionaries. E.g. definitions of the prefix de- may be found in YourDictionary:

1. away from, off: debar, derail

2. down: degrade

3. wholly, entirely: defunct

4. reverse the action of; undo: defrost, decode

Edit: On the second thought, there are some. You can try searching for "Merriam-Webster's a Dictionary of Prefixes, Suffixes, And Combining Forms". I'm not sure if we're allowed to post links to resources, where you can actually download one though, else I'd give you one.