There's only one d, really.

Main Entry: ad·age
Pronunciation: \ˈa-dij\
Function: noun
Etymology: Middle French, from Latin adagium, from ad- + -agium (akin to aio I say); akin to Greek ē he said
Date: 1513
: a saying often in metaphorical form that embodies a common observation

So what if we looked that sh*t up. We did write it out first in our li'l notebook: "Adage," we wrote. "Addage." "F*ck." In that order. For the record, our evaporating gut said go with the one d. But y'all know how we feel about the double, well, nevermind.