a person trained to work in deep-sea vessels for research and rescue purposes.
Origin of hydronaut
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
US navy a person trained to operate deep submergence vessels
Word Origin for hydronaut
C20: from Greek, from hydro- + -naut, as in aeronaut, astronaut
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