'filamentary' originates from Latin, specifically the word 'filamentum', where 'filum' meant 'thread' and the suffix '-ary' meant 'pertaining to'.

'filamentary' changed from the Latin 'filamentum' through Medieval Latin and Old French 'filament' and entered English as 'filament' before the adjective form 'filamentary' developed in Modern English.

Initially, it referred to a 'thread' or 'a small threadlike structure'; over time it evolved into its current meaning of 'threadlike; consisting of filaments'.