feather-light

the compound adjective "feather-light" is a native english formation, combining two old english roots. "feather" derives from proto-germanic feþrō, ultimately from the pie root pet- meaning "to rush, fly." "light" in the sense of "not heavy" comes from proto-germanic linhtaz, from pie h₁lengʷʰ- meaning "lightweight." the logic of the compound is transparently metaphorical, using the archetypal image of a bird's feather—an object of minimal weight and delicate structure—as the ultimate standard for describing something as exceptionally lightweight or gentle. this vivid comparison creates a sensory and intuitive understanding of the quality being described, a common feature in english compounding.

Structure: feather (feather) + light (light) feather (old english, noun, meaning a bird's feather); light (old english, adjective, meaning of little weight)