'fluid' originates from Latin, specifically the word 'fluidus', where 'fluere' meant 'to flow.'

'fluid' changed from Latin 'fluidus' into Middle French/Medieval Latin forms and entered Middle English as 'flud'/'fluid', eventually becoming the modern English word 'fluid'.

Initially, it meant 'flowing' or 'capable of flow'; over time it came to refer both to the property of flowing and to substances that flow ('a fluid').