'two-panel' is a modern English compound formed from the numeral 'two' and the noun 'panel'. 'Two' comes from Old English 'twā' meaning 'two', and 'panel' comes via Middle English from Old French 'panel' (from Late Latin 'pannellus').

'panel' derives from Late Latin 'pannellus' (a diminutive of 'pannus', 'cloth' or 'piece of cloth'), which passed into Old French as 'panel' and then into Middle English as 'panel'; the modern sense extended to any separate section or framed piece (e.g., a door panel, a comic panel). 'Two' comes from Old English 'twā' and retained its basic numeric meaning through Middle English to Modern English.

Initially, 'panel' referred to a piece of cloth; over time it came to mean a distinct section or framed piece (such as in doors, walls, or comics). Combined as 'two-panel', the compound straightforwardly came to mean 'made of two such sections'.