Is it "lawsuit" or "law suit?"

Factual Questions
1

I’m editing an article for our workplace newsletter, and the original author uses both “lawsuit” and “law suit.” Are these interchangeable? Is one more correct than the other? Or are there rules as to when to use “lawsuit” and when to use “law suit?”
(I figured if anyone would know, it would be the dopers…)

Thanks!

2

“Lawsuit”—one word—is the standard usage.

3

The Dictionary of Modern Legal Usage agrees:

Bryan A. Garner, A Dictionary of Modern Legal Usage 507 (2d ed. 1995).

4

Thanks guys!