single combat vs combat

single combat and combat both are nouns.

Word	Noun	Adjective	Verb	Adverb
single combat	Yes	No	No	No
combat	Yes	No	Yes	No

As nouns, combat is a hypernym of single combat; that is, combat is a word with a broader meaning than single combat:

Other hypernyms of single combat include fight, fighting, scrap.

single combat (noun)	combat (noun)
a fight between two people	an engagement fought between two military forces
	the act of fighting; any contest or struggle

single combat (verb)	combat (verb)
	battle or contend against in or as if in a battle