the word "steely" is a transparent english formation, directly combining the noun "steel" with the productive adjectival suffix "-y". the old english root for steel, 'stēle', is of germanic origin, related to dutch 'staal' and german 'stahl', and is thought to be derived from a proto-germanic term meaning "to make firm". the suffix "-y", from old english '-ig', is a common and ancient indo-european derivational element for creating adjectives from nouns. the logic of the word is straightforward: it first described the literal, physical qualities of steel—its hardness, strength, and greyish color. through metaphorical extension, these tangible properties were then applied to describe abstract human qualities, such as a resolute will or a cold, unemotional demeanor, giving us the modern figurative senses.

Structure: steel (metal) + y (adjective suffix) steel (from old english 'stēle', 'stȳle', meaning the hard metal alloy) + y (from old english '-ig', an adjective-forming suffix meaning "composed of, characterized by, or resembling").