'disadvantageous' originates from the prefix 'dis-' meaning 'not' or 'opposite of', combined with 'advantageous', which comes from the Old French 'avantage', meaning 'advantage'.

'advantageous' evolved from the Old French word 'avantageux', which was adapted into Middle English as 'avantageous', eventually becoming 'advantageous' in modern English.

Initially, it meant 'having an advantage', but with the prefix 'dis-', it evolved to mean 'not having an advantage' or 'unfavorable'.