'two-modal' originates from English compound elements 'two' and 'modal'; 'two' ultimately comes from Old English 'twā' meaning 'two', and 'modal' derives from 'mode', from Latin 'modus', where 'modus' meant 'measure, manner'.

'mode' entered English via Old French 'mode' from Latin 'modus'; the adjective 'modal' developed from 'mode', and the compound 'two-modal' formed in modern English usage to describe distributions or systems with two modes.

Initially, 'modal' related to manner, form, or mode in a general sense; over time, especially in statistics and signal/process descriptions, it came to refer specifically to the 'mode' of a distribution, so 'two-modal' now means 'having two modes'.