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Thetis

American  
[thee-tis] / ˈθi tɪs /

noun

Classical Mythology.
  1. a Nereid, the wife of Peleus and the mother of Achilles.


Thetis British  
/ ˈθiːtɪs /

noun

  1. one of the Nereids and mother of Achilles by Peleus

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012