Other forms: fettled; fettling; fettles
Fettle is the state or condition you're in, especially if it's positive. You might describe your bouncy, healthy puppy as being in fine fettle.
You'll almost always see the adjective "fine" describing the noun fettle. Being in fine fettle means feeling good, being healthy, or having an energetic approach to something. A powerful speaker who gives a particularly rousing speech is in fine fettle, and an eighty-year-old marathon runner is also in fine fettle. In 1700s Lancashire dialect, fettle meant "to make ready," or "to prepare for battle," from the Old English word fetel, "belt or girdle."