snake in the grassn. pl. snakes in the grass See snake.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.snake? in the grass` n. 1. a treacherous person, esp. one who feigns friendship. 2. a concealed danger. [1690?1700] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.