egg on - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Incite, urge ahead, provoke, as in Jack is always egging me on to drive faster, or Seemingly quiet, Margo actually eggs on Donald to quarrel with his staff. This expression has nothing to do with hen's eggs but comes from an Old Norse word, eggja, “to edge.” Both edge on and egg on were used interchangeably, but today the latter is preferred. [c. 1200]