'greyish' originates from English, specifically combining the adjective 'grey' (Old English 'grǣg') and the suffix '-ish' (Old English '-isc' / Old Germanic), where 'grǣg' meant 'grey' and '-ish' meant 'having the quality of' or 'somewhat like'.

'greyish' developed from the older English adjective 'grey' (Middle English 'grei', 'grey' from Old English 'grǣg') plus the adjective-forming suffix '-ish' (from Old English '-isc'). Over time the compound form became the modern English 'greyish'.

Initially it meant 'having the quality of grey' in a straightforward, literal sense; over time it has retained that core meaning and also acquired figurative uses meaning 'somewhat dull or gloomy'.