Subaltern
Definition: a person who is lower in position or rank; a subordinate
Why I Looked It Up
This came up a couple times in a book about World War 1, always in the context of British military officers. I dismissed it as a British-ism, but then found it again in a book about American history.
Jackson subaltern Sam Houston, the first elected president of Texas..
Houston served under General Jackson in the War of 1812.