hot-air

The compound "hot-air" is a metaphorical extension of a literal physical phenomenon. Literally, it refers to heated air, such as that used in a hot-air balloon. The figurative meaning, denoting empty or exaggerated speech, emerged in the late 19th century. The logic is that such talk is insubstantial, full of sound and warmth but lacking in solid content or truth, much like the hot air that rises but is intangible. This evolution from a concrete physical description to an abstract critique of language is a classic example of semantic shift through metaphor.

Structure: hot (having a high temperature) + air (the invisible gaseous substance) - hot: From Old English hāt (hot, fervent, fierce), of Germanic origin. Functions as an adjective describing a quality. - air: From Old French air, from Latin āēr, from Greek aēr (air, atmosphere, mist). Functions as a noun, the object being described.