1. Used to attract attention or to express surprise, appreciation, wonder, or pleasure: "Oh, hey, you saw that ninety-nine-yard punt return in the Super Bowl? Wow, so did I!" (Don Pfarrer).

2. Used to express greeting.

[Middle English hei.]

Word History: A word sounding like hey has been used in English since Middle English times—Middle English hei was used to call someone's attention and also to express anger, derision, or opposition. Hei could also be used to urge dogs on during the hunt and to express grief or concern—this was probably a long, drawn out hey.... The word probably originated simply as an imitation of the various loud, meaningless exclamations that people may utter when they are surprised or trying to attract the attention of others. Nowadays, we find the word hey used in various other ways, as for emphasis in the expression but hey. It is also used as a greeting, the short, colloquial equivalent of How are you? and thus close kin to the informal salutation hi. Hi appears to have arisen in North American English in the middle of the 1800s. However, hey seems to be replacing hi in many situations today. Until recently, the greeting hey had a distinctly Southern flavor. The national survey conducted in the 1960s by the Dictionary of American Regional English found hey as a greeting restricted chiefly to Arkansas, Louisiana, Mississippi, Florida, Georgia, and the Carolinas. The friendly hey has since spread throughout the United States. Interjections sounding like hey are also used as greetings in other languages, such as Swedish hej.

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.

interj

1. an expression indicating surprise, dismay, discovery, etc, or calling for another's attention

2. South African an exclamation used for emphasis at the end of a statement, or alone to seek repetition or confirmation of another person's statement

3. hey presto an exclamation used by conjurors to herald the climax of a trick

[C13: compare Old French hay, German hei, Swedish hej]

Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

(used as an exclamation to call attention or to express pleasure, surprise, bewilderment, etc.)

[Middle English hei]

Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.