rock-hard

The compound adjective "rock-hard" is a straightforward formation from two native English elements. The noun "rock," denoting a large stone or mass of mineral matter, has been used since Old English to symbolize ultimate solidity and durability. The adjective "hard," also from Old English, describes a fundamental physical property of firmness and resistance. When combined in the 19th century, the phrase creates a powerful, hyperbolic metaphor, comparing an object's extreme and unyielding firmness directly to the perceived absolute hardness of stone. This compounding logic is transparent, leveraging the core, concrete meanings of both words to intensify the descriptive quality.

Structure: rock (rock) + hard (hard) - rock: From Old English rocc, of unknown origin, but likely related to Medieval Latin rocca. Functions as a noun used attributively to denote the quality of being like rock. - hard: From Old English heard, of Germanic origin; related to Dutch hard and German hart. Functions as an adjective meaning solid, firm, or resistant to pressure.