field of battle vs battlefield

field of battle and battlefield both are nouns.

Word	Noun	Adjective	Verb	Adverb
field of battle	Yes	No	No	No
battlefield	Yes	No	No	No

As nouns, field of battle and battlefield are synonyms defined as:

field of battle and battlefield: a region where a battle is being (or has been) fought

Other synonyms of field of battle include battleground, field, field of honor.

field of battle (noun)	battlefield (noun)
a region where a battle is being (or has been) fought	a region where a battle is being (or has been) fought