A more thorough explanation:

Definition: A civilian is a person who is not serving in the military. It can also refer to a lawyer who practices civil law or a scholar who studies civil or Roman law.

Examples:

• John decided not to join the army and instead became a civilian.
• As a civil lawyer, Sarah specializes in cases that involve disputes between individuals or organizations.
• Professor Smith is a renowned civilian who has written extensively on Roman law.

The first example illustrates the primary definition of a civilian as someone who is not in the military. The second and third examples show the secondary definitions of a civilian as a lawyer or scholar who specializes in civil or Roman law.