veteran

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A person who has served in the armed forces.
• noun An old soldier who has seen long service.
• noun A person who is long experienced or practiced in an activity or capacity.

from The Century Dictionary.

• Grown old in service.
• Hence— Practised and skilful.
• Entitled to consideration and allowance on account of long service.
• In milit. matters, practised and accustomed to war, as distinguished from raw, newly enlisted, etc.
• Long-continued; of, pertaining to, or characteristic of a veteran or veterans.
• noun One long practised, and therefore skilled and trustworthy, or entitled to consideration on account of past services; especially (military), a veteran soldier. See I., 2 .
• Same as veteranize.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who has been long exercised in any service or art, particularly in war; one who has had much experience, or has grown old or decrepit in service.
• adjective Long exercised in anything, especially in military life and the duties of a soldier; long practiced or experienced

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A person with long experience of a particular activity.
• noun A person who has served in the armed forces, especially an old soldier who has seen long service.
• adjective Having had long experience, practice, or service.
• adjective Of or relating to former members of the military armed forces, especially those who served during wartime.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a person who has served in the armed forces
• adjective rendered competent through trial and experience
• noun an experienced person who has been through many battles; someone who has given long service
• noun a serviceman who has seen considerable active service