One, such as a person or a combat vehicle, that takes part in armed strife.(noun)
Engaging in armed strife.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "combatant" in a sentence
"Designation as an enemy combatant is a classic example."
"Being treated as a combatant is a far less offense."
"But the questions of categorization posed by Guantánamo -- including the question of who may be treated as the legal equivalent of a "combatant" -- will retain their significance long after the doors to that facility are shuttered."