By Doina Chiacu and Emily Stephenson

WASHINGTON (Reuters) - Republican presidential candidate Donald Trump used a vulgarity to describe Hillary Clinton's loss to Barack Obama in the 2008 Democratic presidential race and then derided her over the time she took for a bathroom break during a debate.

Trump's off-color comments about the Democratic front-runner at a campaign appearance on Monday night came a day after he called Clinton a liar for saying his proposal to ban entry of all foreign Muslims to the United States aided Islamic State's propaganda efforts.

"She was going to beat Obama," Trump said of Clinton, speaking in Grand Rapids, Michigan. "... She was going to beat - she was favored to win - and she got schlonged. She lost."

"Schlong" is a Yiddish slang term for a man's genitals.

Trump, leading the field to be the Republican nominee in the November 2016 presidential election, also made a reference to Clinton returning to the stage late after a bathroom break during a Democratic debate on Saturday night.

"I thought she gave up," Trump said. "Where did she go? Where did Hillary go? They had to start the debate without her. Phase II. I know where she went. It's disgusting. I don't want to talk about it," Trump said.

Clinton, answering a question about bullying at an event in Iowa, did not name Trump but said she was used to people saying "terrible things" about her.

"It's important to stand up to bullies wherever they are, and why we shouldn't let anybody bully his way into the presidency because that is not who we are as Americans," Clinton said, according to video that aired on MSNBC on Tuesday.

Jennifer Palmieri, Clinton's communications director, also tweeted a scathing response.

"We are not responding to Trump but everyone who understands the humiliation this degrading language inflicts on all women should," Palmieri said.

News reports after Saturday's debate, explaining Clinton's delay getting back to the stage, said the women's bathroom was farther away than the men's room.

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A Reuters/Ipsos poll released on Monday found that Trump would lose to Clinton in a hypothetical head-to-head contest if the presidential election were held now.

Trump, whose supporters admire him for plain speaking, appeared to struggle to win women's support in a Quinnipiac Poll released on Tuesday. Six in 10 women said they would be "embarrassed" if the real estate tycoon were president, compared to four in 10 men, the poll found.

'DRUGGED OUT'

Trump's blunt and sometime outrageous style and comments about Hispanics, women, Muslims and his rivals for the nomination have set much of the tone for the Republican race. He is also known for pouring scorn on hecklers at his events, as he did Monday night. Some were ejected from the venue and Trump suggested they might be "drugged out." He chided another group for being "so weak" they would not resist security guards' directions to leave.

Trump's comments about Clinton were not the first time he has veered into vulgarity. In 2011, he used the term "schlonged" in a Washington Post interview to refer to a Republican candidate who lost to a Democrat in a surprise upset. Both candidates in that race were women.

After a televised debate in August, he posted Twitter messages criticizing Fox News moderator Megyn Kelly and made comments in a television interview that were widely interpreted as referring to her menstrual cycle. He denied that was his intention.

Trump, 69, said last month that Clinton, 68, did not have strength or stamina to be president, and he also has called her the worst U.S. secretary of state during her time in the post from 2009 to 2013.

He has frequently mocked his rivals for the Republican nomination for their lower standing in the polls, often focusing on Jeb Bush, who he describes as "low energy." Trump was quoted in Rolling Stone magazine in September talking about the appearance of Carly Fiorina by saying, "Look at that face. Would anyone vote for that?"

For more on the 2016 presidential race, see the Reuters blog, “Tales from the Trail” (http://blogs.reuters.com/talesfromthetrail/)

(Additional reporting by Mohammad Zargham; Editing by Bill Trott and Frances Kerry)