grass snaken. Any of several greenish nonvenomous snakes, especially Opheodrys vernalis of eastern North America or Natrix natrix of Europe.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.grass snake n 1. (Animals) a harmless nonvenomous European colubrid snake, Natrix natrix, having a brownish-green body with variable markings 2. (Animals) any of several similar related European snakes, such as Natrix maura (viperine grass snake) Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014grass? snake` n. any of various small slender snakes of North America, as the garter snake or green snake. [1835?45, Amer.] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.