'lightweight' originates from English, formed as a compound of 'light' + 'weight', where 'light' meant 'not heavy' and 'weight' meant 'mass or heaviness'.

'light' comes from Old English 'léoht' meaning 'not heavy' (also 'bright'), and 'weight' from Old English 'wǣ̄ġt' meaning 'heaviness'; the compound 'light-weight' appeared in English (written with a hyphen) and later solidified as 'lightweight' in modern usage. The sporting sense (weight classes) developed in the 19th century.

Initially it meant 'having little weight' (physical sense); over time it extended to mean 'of little importance or substance' and also became a noun denoting competitors in a light weight class.