An adage is a saying. Moms and dads love adages such as "early to bed, early to rise" and "an apple a day keeps the doctor away."
The noun adage comes from the Latin root aio, meaning "I say." Like a proverb, an adage can be true or not so much. It's a folksy saying that's been passed around for so long that it doesn't even matter if it's true anymore. Adages can be wise and wisecracking, such as this quote from Alice Roosevelt Longworth: "I've always believed in the adage that the secret of eternal youth is arrested development." There's a Book of Proverbs in the Bible, but adages can show up anywhere, even cross-stitched on a pillow.