'reddish-orange' originates from Modern English as a compound of 'reddish' and 'orange', where 'reddish' is formed from 'red' + the suffix '-ish' (meaning 'somewhat' or 'like') and 'orange' comes from Old French/Medieval Latin for the fruit/color.

'red' comes from Old English 'rēad'; 'orange' entered English via Old French 'orenge' from Medieval Latin 'aurantium' and ultimately from Arabic/Persian forms of the word for the fruit (e.g. Arabic 'nāranj'). The compound 'reddish-orange' was created in Modern English by combining 'reddish' and 'orange' to describe an intermediate tint.

Initially 'red' and 'orange' referred to separate colors (and 'reddish' meant 'somewhat red'); over time the compound came to denote a distinct perception: an orange color with a clear red tint or a hue between red and orange.