The term 'SHUT YER ___!' is a phrase used to express annoyance or frustration. The two crossword solutions for this term are YAP (3 letters) and TRAP (4 letters). YAP is an informal verb meaning to talk incessantly, often in a loud or annoying manner. TRAP is a noun that refers to a device or enclosure used to capture animals or people. Therefore, the phrase 'SHUT YER ___!' can be interpreted as telling someone to stop talking or to be quiet.