Previous research has suggested that defeat (conceptualized as a failed social struggle) and entrapment (conceptualized as a perceived inability to escape from aversive situations) form a single construct that reliably predicts psychopathological outcomes in clinical and community settings. However, scales designed to assess defeat and entrapment measure the constructs separately, whereas recent evidence suggests a single scale would be appropriate. Existing scales may also be too lengthy to have clinical utility. The present study developed and evaluated a scale that measured both defeat and entrapment. Exploratory and confirmatory factor analyses demonstrated that defeat and entrapment were best defined by a single factor, and 8 items were selected that best represented this construct to form the short scale. The scale had high internal consistency (α = .88 to .94), showed criterion validity with hopelessness (r = .45 to .93) and incremental validity for caregiver burden when controlling for depression and positive symptoms of psychosis when controlling for hopelessness (β = .45 to .60). Additionally, the scale had excellent test-retest reliability using single measures absolute agreement intraclass correlation coefficients across 12 months (ricc = .88 to .92) within 4 samples: people with posttraumatic stress disorder, people with psychosis, care home employees, and people from community settings. The scale demonstrated known group validity through discrimination between clinical and nonclinical groups of participants. This scale could be implemented within therapeutic settings to help clinicians identify patients experiencing defeat and entrapment, and incorporate these factors into their clinical assessment and case formulations for treatment.