Secrete is all about secrets. It means both "to hide" and "to release." When you squeeze a lemon, it secretes juice. When you stuff your money in a mattress, you secrete it there.
It's easy to remember that secrete's all about secrets when you see the word secret inside secrete. Imagine the first person who squeezed a lemon and secreted the juice. Probably felt like he'd discovered a secret stash of citrus goodness. If he was greedy, maybe he gathered all the lemons he could find and secreted them away in a box so no one else would learn the secret of the juice-secretion.