"As many of you know, I said something hateful on the air Wednesday night," Brennaman said in a long op-ed posted on Cincinnati.com ... "something no one should ever say."

Brennaman says he didn't realize the homophobic f-word was "so rooted in hate and violence" -- and says he vows to never use it again.

"I cannot erase what I have done," Thom said. "The only thing I can do is humbly apologize, accept the consequences of my actions and resolve to be better and behave differently from now on."

Brennaman directly addresses the LGBTQ+ community ... saying, "I am truly and deeply sorry. You should never be denigrated with crude and hateful language. I failed you, and I cannot say enough how sorry I am."

Brennaman also says he has already spoken with MLB exec Billy Bean -- who's openly gay -- and Bean has agreed to work with him on how to "become a more informed person."

"I immediately plan to participate in diversity, equity and inclusion training and have reached out to PFLAG for resources and guidance," Thom said.

Brennaman -- who's been suspended by the Reds and pulled from the "NFL on FOX" schedule -- says he doesn't know if he'll ever work in broadcasting again ... but says this incident has forced him to "reflect on who I am and how I am want to be seen and thought of."