'barnacle' originates from Medieval Latin, specifically the word 'bernicula' (also seen as 'bernaculum' in medieval sources), where the root referred to a kind of small goose or bird.

'barnacle' changed from Medieval Latin 'bernicula' into Old French forms (such as 'bernoucle') and then into Middle English as 'barnacle'; the word was applied to the barnacle goose and later to the crustacean that attaches to ships, and finally to the verb meaning 'to become covered with barnacles'.

Initially, it referred to a bird (the barnacle goose) or a small goose; over time the meaning shifted to the shellfish (the crustacean) and then to the figurative/verb sense 'to be covered with barnacles' or 'to attach barnacles to'.