'sooty' originates from the noun 'soot' + the adjectival suffix '-y' in Middle English, where 'soot' referred to the black powder produced by burning.

'sooty' developed in Middle English from Old English 'sōt' (or 'sot') meaning 'soot'; the suffix '-y' (from Old English '-ig') formed adjectives meaning 'characterized by' or 'full of', producing 'sooty'.

Initially it literally meant 'full of or covered with soot', and over time it has kept that primary meaning while also being used more generally for 'dark' or 'smoky' in color or tone.