Wiktionary
rear admiral (lower half)
n. 1 (context US military nautical English) A commissioned officer in the United States Navy, United States Coast Guard, National Oceanic and Atmospheric Administration Commissioned Corps, or Public Health Service Commissioned Corps of a grade superior to a captain and junior to a rear admiral (upper half). A rear admiral (lower half) is equal in grade or rank to an United States Army, United States Marine Corps, or United States Air Force brigadier general. 2 (context US military nautical English) A naval officer of equivalent grade or rank in the navy of other countries, such as commodore.