1. adjective [ADJ after v, v-link ADJ, ADJ n]
If something is unguarded, nobody is protecting it or looking after it. ⇒ I should not leave my briefcase and camera bag unguarded.
2. adjective [usu ADJ n] If you do or say something in an unguarded moment, you do or say it carelessly and without thinking, especially when it is something that you did not want anyone to see or know. ⇒ The photographers managed to capture Jane in an unguarded moment. ⇒ He was ambushed by a reporter into an unguarded comment.
COBUILD Advanced English Dictionary. Copyright © Harper Collins Publishers