Definition: Not everything that looks expensive or precious actually is.
Origins: If you, like me, were raised on 90’s one hit wonders and the first thing that this phrase brings to mind is the refrain from Smash Mouth’s 1999 song, “All Star,” than I applaud your memory. However, I hate to be the one to tell you that the actual song words mean the opposite of this idiom. The refrain actually goes like this: “Hey now you’re an All Star get your game on, go play/ Hey now you’re a Rock Star get the show on get paid/ And all that glitters is gold/ Only shooting stars break the mold.” The song leaves out “not,” which changes the entire meaning and implies that all shiny precious things are just that. The origins for the saying “all that glitters is not gold” can be traced as far back as the 12th century where French theologian Alain de Lille wrote a variant of the saying: “Do not hold everything gold that shines like gold.” After de Lille, other authors, poets and playwrights such as Chaucer, Cervantes, and Shakespeare have taken on the saying in various forms. The present form of the phrase originated in 1687 when English author John Dryden stated, “All, as they say, that glitters is not gold,” in The Hind and the Panther.
Hendrickson, Robert. Words and Phrase Origins. 3rd ed. New York: Facts On File, 2004, 18.