Frank Ocean Wants Dad's Defamation Suit Thrown Out Because He Claims |

Frank Ocean isn't backing down from his father -- who sued his son for saying he used a homophobic slur -- he's doubling down, insisting dear ol' dad said the word.

The singer responded to the lawsuit, saying he doesn't deny writing the Tumblr post last summer after the Orlando nightclub shooting. Frank recounted a time his father called a transgender waitress a "f****t" when he was a kid.

According to the docs ... Ocean claims his statements are true -- and that's all the defense he needs to fight his father's defamation suit.

Frank actually wants the court to dismiss the case, and he's demanding dad cover his court costs.