fluke (1) Look up fluke at Dictionary.com
"flat end of an arm of an anchor," 1560s, perhaps from fluke (3) on resemblance of shape, or from L.Ger. flügel "wing." Meaning "whale's tail" (in plural, flukes) is 1725.
fluke (2) Look up fluke at Dictionary.com
"lucky chance," 1857, originally a lucky shot at billiards, of uncertain origin.
fluke (3) Look up fluke at Dictionary.com
"flatfish," O.E. floc "flatfish," related to O.N. floke "flatfish," flak "disk, floe" (see flake). The parasite worm (1668) so called from resemblance of shape.