The word is a modern English compound formed by appending the native adjectival suffix "-less" to the noun "symptom." The noun "symptom" entered English in the late medieval period from Latin symptoma, which itself originated from the Greek symptōma, meaning "anything that has befallen one," derived from sympiptein ("to fall together, coincide"). The Greek root combines syn- ("together") and piptein ("to fall"), metaphorically describing concurrent signs that befall a patient. The suffix "-less," with its Old English origin meaning "devoid of," directly and logically negates the core noun, creating a transparent medical term meaning "devoid of symptoms."

Structure: symptom (sign of illness) + less (without) - symptom: From Greek symptōma (a happening, accident, symptom), via Late Latin and Middle English. Functions as the core noun root. - less: From Old English -lēas (devoid of, free from), a native English suffix forming adjectives meaning "without."