fluke

(noun) a stroke of luck. Synonyms: good luck, good fortune.

(noun) a barb on a harpoon or arrow.

(noun) flat bladelike projection on the arm of an anchor. Synonyms: flue.

(noun) either of the two lobes of the tail of a cetacean.

(noun) parasitic flatworms having external suckers for attaching to a host. Synonyms: trematode, trematode worm.