Foam or bubbles formed on top of a liquid, often airy and insubstantial; also can mean trivial or worthless talk.
From Old English 'froth' and Old Norse 'froda,' both referring to foam or bubbles. The metaphorical meaning of 'empty talk' developed naturally from the insubstantial nature of foam.
Shakespeare used 'froth' to describe shallow people and empty words, and the metaphor stuck so well that we still call nonsense 'froth'—five centuries later, foam remains the perfect image for something that looks substantial but isn't.
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