'unclearly-expressed' originates from the combination of 'un-' meaning 'not', 'clear' from Latin 'clarus' meaning 'bright', and 'express' from Latin 'exprimere' meaning 'to press out'.

'unclearly-expressed' evolved from the Middle English 'clere' and 'expressen', eventually forming the modern English compound adjective.

Initially, it meant 'not bright or not pressed out clearly', but over time it evolved into its current meaning of 'not clearly articulated'.