'filiform' originates from Latin, specifically the Late Latin word 'filiformis', where 'filum' meant 'thread' and '-formis' meant 'shape or form.'

'filiformis' in Late Latin passed into New Latin as 'filiformis' and was adopted into English as 'filiform' (chiefly in scientific usage) by way of scholarly Latin/vernacular usage.

Initially, it meant 'having the form of a thread,' and over time this meaning has remained largely stable, used chiefly in technical and scientific contexts to mean 'threadlike.'