Sixteenth-century English revelers toasting each other's health sometimes drank a brimming mug of spirits straight to the bottom—drinking "all-out," they called it. German tipplers did the same and used the German expression for "all out"—gar aus. The French adopted the German term as carous, using the adverb in their expression boire carous ("to drink all out"), and that phrase, with its idiomatic sense of "to empty the cup," led to carrousse, a French noun meaning "a large draft of liquor." And that's where English speakers picked up carouse in the 1500s, first as a noun (which later took on the sense of a general "drunken revel"), and then as a verb meaning "to drink freely."