When you express your extreme disapproval of something, that's deprecation. Your health teacher's deprecation of sugary snacks may change your eating habits — or it might just make you feel a little guilty for enjoying your jelly beans.
Deprecation can take many forms, from a blistering opinion piece in the newspaper criticizing a political figure to your mom's subtle facial expression that tells you she wishes you'd worn a clean shirt to church. Self-deprecation is when you criticize yourself or put yourself down. A more old-fashioned meaning of this word is "a prayer to avert evil," from the Latin deprecari, "to avert by prayer" or "to pray away."