Say wha'?

This was part of a conversation at breakfast yesterday that cracked all of us up. The girls were talking about words and their meanings.

Aubrey: Sit down and sit up both mean to sit, but mean different things. One means to sit when someone is standing and the other to sit when you're laying down. Stand up and stand down have complete different meanings that aren't related to each other at all.

Lauryn (5 yo): What does "stand down" mean?

Aubrey: "Stand down" means to surrender.

Lauryn (looking completely puzzled): In Latin?