Donald J. Trump on Monday night mocked Hillary Clinton for using the bathroom during last weekend’s Democratic presidential debate and employed a vulgar term to describe her defeat to Barack Obama in the 2008 primary.

“She was favored to win, and she got schlonged,” Mr. Trump, using a boorish word for a penis, said at a rally in Grand Rapids, Mich.

Mr. Trump is no stranger to vulgarity on the campaign trail. But his word choice at a rally on Monday in Michigan found new linguistic territory for a businessman who has tested every boundary in modern politics.

The Republican has ramped up his criticism of Mrs. Clinton but largely steered clear of attacks that are overtly gendered. On Monday, that changed.

Mr. Trump made light of Mrs. Clinton’s bathroom break during Saturday’s debate, which made her arrive late to the lectern after a commercial break.

“I know where she went — it’s disgusting, I don’t want to talk about it,” Mr. Trump said.

Referring to Mrs. Clinton’s delayed arrival — aides attributed it to the long walk to the women’s room, which was farther from the stage than the men’s room — Mr. Trump took a conspiratorial tone. “Wasn’t that a weird deal?” he wondered to the audience.

On Tuesday morning, a spokeswoman for Mrs. Clinton’s campaign addressed the remarks on Twitter.