An addition or small amount of something white is a whit.
When we talk about paint or other finishes, a whit can mean a small amount added to make it lighter. So if someone says "I added a bit of whit to the paint," they're talking about adding just enough to give it a slightly different tone. In conversation, people often use whit as an informal way to say something is a little bit of this or that - for example, "The recipe calls for just a whit of sugar." It's not used in formal writing, but it's common in everyday speech and can be understood by most people.
The smallest part or particle imaginable; an iota.
Example: He worked tirelessly to collect and wind a ball of string eight feet around, and it matters not one whit.
