'ill-expressed' originates from English, specifically the words 'ill' and 'expressed', where 'ill' originally meant 'bad' (i.e. 'poorly') and 'expressed' comes from Latin 'exprimere' (ex- + primere) meaning 'to press out'.

'expressed' changed from Latin 'exprimere' into Old French forms (e.g. 'esprimer') and then into Middle English 'expressen', from which the past participle 'expressed' developed; 'ill' comes from Old English words meaning 'bad' (e.g. 'yfel') and later combined with past participles to form compounds like 'ill-advised' or 'ill-expressed'.

Initially, the Latin root meant 'to press out' and French/Middle English forms meant 'to state' or 'to convey'; combined with 'ill' (originally 'bad'), the compound came to mean 'stated badly' or 'poorly conveyed' in modern usage.