The term "trans-fatty" is a modern scientific compound. The prefix "trans-," borrowed directly from Latin, is used in chemistry to specify a geometric isomerism where hydrogen atoms attached to carbon atoms are positioned on opposite sides of a carbon-carbon double bond. This spatial configuration contrasts with the "cis-" arrangement. The base "fatty" derives from the common English word for lipid material. Thus, "trans-fatty" literally describes a type of fat molecule with this specific "across" configuration, which was later found to have negative health implications, distinguishing it from other unsaturated fats.

Structure: trans (across) + fatty (fat) - trans: From Latin, meaning "across, beyond, through." In chemistry, it denotes a molecular configuration where atoms are on opposite sides of a double bond. - fatty: From English "fat" (from Old English fǣtt, meaning "fatty, plump") + the adjectival suffix "-y," meaning "characterized by or full of."