A soldier.
Specifically, a marine.
A person who has served in the armed forces, especially an old soldier who has seen long service; also called a war veteran to distinguish from veterans who weren't in armed conflict.
A person with long experience of a particular activity.
A group, animal, etc. with long experience of a particular activity.
Having had long experience, practice, or service.
Of or relating to former members of the military armed forces, especially those who served during wartime.