When I was perusing the works of Thomas Wyatt, looking for poem structures to appropriate, I came across these lines:
Yet though thy chain hath me enwrapt,
Spite of thy hap, hap hath well hapt.
I had never seen the word “hap” before, and so, being a lover of etymology, I went to look it up. It turns out it means “luck”, so if you are “happy” you are lucky. It shows up in lots of other words, of course: perhaps (by way of luck), mishap (bad luck), happen (to come about by luck), hapless (without luck). A neat little nugget that I will keep my eye out for in the future.