Miley's little sis threw her support behind Styles after his Vogue spread last month -- wearing a dress -- prompted Owens to verbally attack Harry for not being "manly."

Problem is, Noah's choice of words were racially charged -- her IG story post said Styles wears a dress "better than any of u nappy ass heauxz."

If you didn't know, Owens is Black ... something Noah certainly knew, so it's clear she needs a history lesson about the racist undertones of the word "nappy." It sounds like someone gave it to her, because she got a ton of backlash on social media ... and is now apologizing.

She says, "I am mortified that I used a term without knowing the context and history, but I know now and I am horrified and truly sorry. I will never use it again. Thank you for educating me."

Lesson learned ... however, it's not like Harry needed the help, anyway.

He'd already responded to Owens' dig, by sharing a new photo of himself in a powder blue suit eating a banana, captioning it with Candace's own words ... "Bring back manly men."

Owens claimed Styles' clapback is proof she inspires global conversation, tweeting ... "When people try to tell me I don’t have influence, and then [Styles] dedicates an entire post to my tweet."