A growing moon is said to be "waxing" and a shrinking moon is said to be "waning"

1. A growing moon is said to be "waxing" and a shrinking moon is said to be "waning." The left side of the picture is of a waxing moon and the right is of a waning moon. A mnemonic device to help remember the waxing vs. waning phase is to think of the moon as making a "C" shape during the waning phase and associate the "C" with the word "Ceasing," a synonym for waning.