1. Greek Mythology. A giant with 100 eyes who was made guardian of Io and was later slain by Hermes.
2. An alert or watchful person; a guardian.

[Latin, from Greek Argos.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.