Thesaurus was the commercial where it has the thesaurus on M&M's backwards which made the name Plain to Milk Chocolate in 2001.
Commercial First Aired: September 25, 2000
Commercial Last Aired: October 9, 2001
Red: Well, what's it say?
Patrick: Plain. Ordinary, low, simple, dull, boring, average, common, video, verb.
(Red checked the M&M's backwards what it says, "Plain.")
Red: Oh, man. Plain's the worst name ever.
Patrick: No, that would be, "Lucy."
(Screen shows the M&M's bag' backwards what it says, "Plain", and then the bag spins into normal.)
Voice: M&M's, same great chocolate. Much better name.