Word(s) of the Day: Thank-you and Thank-you-ma'am

I’ve been wondering about what to do with the phrase “thank you” when it’s used as a noun (“a big thank you goes out to Bill”) or as an adjective (“I sent him a thank you card”) and, like any editor or writer should, I decided to check the all-powerful Merriam-Webster. 

This is what I found:

thank-you n [fr. the phrase thank you used in expressing gratitude] (1792): a polite expression of one’s gratitude

So, yes, “thank-you” is the correct form for a noun; and just to make myself feel better, I also checked the Corpus of Contemporary American English, which confirmed Webster’s. (Or I think it did. I am not very good at using COCA yet, but it is a super-cool resource.) Neither source said anything about the adjective form of “thank you,” but since it’s pretty standard to hyphenate two-part adjectives (like I just did there, ha!) then I think I’m safe to use “thank-you note.”

But the fun part comes next. When I looked up “thank-you,” I happened to glance at the entry below it, and this is what I found.

thank-you-ma’am n [prob. fr. its causing a nodding of the head] (1849): a bump or depression in a road; esp: a ridge or hollow made across a road on a hillside to cause water to run off

SWEET. New vocabulary word for the win. I love the dictionary. 

Have you come across any awesome new words lately?