Both meanings, can work.

@Castlepaloma An oxymoron has to be at least two words...

[prowritingaid.com]

@ChestRockfield

An oxymoron is a common rhetorical device that combines two or more words with contradictory meanings into a single phrase.

How can one be a lover and a fighter? When fighting is more likely to harm someone mentally or physically or both. I think of love as expanding and growth. Where fighting is more destructive and contracting

@Castlepaloma Speaking strictly about this question you posed, "Is the word lover an oxymoron for fighter" one word can't be an oxymoron, and it makes even less sense to say a single word is an oxymoron for another single word. Words or even phrases aren't oxymorons for other words or phrases. They are either oxymorons because they contain seemingly contradictory words, or they are not. Again, I think you're thinking of contronym.