Etymology: First coined to describe a hot meal, the term’s sloppy connotations quickly morphed from food-related to figurative when it came to reference a chaotic yet appealing individual.

Meaning: Stand-up comedian Amy Schumer has amassed a multimillion-dollar fortune through being a hot mess. Her ribald humor—which riffs on binge-drinking, body parts and bad sex—has established this identity as her shtick, so much so that billboards advertising her show, Inside Amy Schumer, were branded with the phrase.

Ask a soldier in the late 19th century to describe a hot mess, however, and he’d launch into details of the canteen meal he’d just scoffed. A literal descriptor of a warm, mushy meal prepared in bulk, the word’s origins can be traced to the Latin root, “missus,” meaning...