(bär′nə·kəl) noun
1. A marine shellfish (order Cirripedia) that attaches itself to rocks, ship bottoms, etc.; especially, the rock barnacle (Balanus balanoides) and the goose barnacle (Lepas fascicularis), the latter so called because the barnacle goose was once supposed to hatch from it.
2. A European wild goose of northern seas (Branta leucopsis): also barnacle goose.
3. Something or someone that clings tenaciously; a persistent follower; a hanger-on. [ME bernacle; origin uncertain]
—bar′na·cled adjective

(bär′nə·kəl) noun
Usually plural An instrument for pinching the nose of an unruly horse. [OF bernacle, dim. of bernac a bit]