Save Our Servicemembers Act of 2021 This bill requires the Office of the Under Secretary of Defense for Personnel and Readiness within the Department of Defense (DOD) to evaluate and standardize DOD's suicide prevention efforts. Specifically, the bill directs the Defense Suicide Prevention Office to collaborate with each military department to (1) develop and implement a process to ensure that individual nonclinical suicide prevention efforts are assessed for effectiveness, and (2) develop consistent suicide-related definitions for use throughout DOD. The bill also requires the use of such suicide-related definitions in any updated policies of DOD or each military department.