The Collaborative International Dictionary of English v.0.48:

Requin \Re"quin\ (r?"kw?n), n. [F., fr. reqiem a Mass sung for
   the dead. See Requiem.] (Zool.)
   The man-eater, or white shark (Carcharodon carcharias); --
   so called on account of its causing requiems to be sung.
   [1913 Webster]