Feisty describes someone who has or shows a lively aggressiveness especially in being unafraid to fight or argue. In some regions of the US, feisty may also be used as a synonym of fidgety, quarrelsome, or frisky.

// Even her opponents admire her feisty spirit.

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"Hummingbirds may be tiny, but the feisty birds can be fearless. A video ... shows a falcon eating a dragonfly while perched on a tree. Then, out of nowhere, a hummingbird flies into the frame and starts flitting around the bird of prey." — Shelby Slade and Tiffany Acosta, The Arizona Republic, 26 Sept. 2024

In some parts of the southern United States, the word feist (pronounced to rhyme with heist) has been used since the 18th century as a term for a small dog used in hunting more diminutive game animals (such as squirrels). The word comes from the much older, now obsolete word fisting (pronounced as “feisting” would be) meaning “breaking wind,” which was used scornfully in the 16th and 17th centuries to describe gassy pooches. Feisty developed in the late 19th century, its flatulent origin lost, but its small-dog association still visible with a squint: the term conveys the spunk and determination that one may associate with a dog that manages to make its presence known, through its bark or its bite—or perhaps even its indifference to olfactory decorum—despite its small size.