Trump is known for blunt, straightforward language, despite occasionally criticising rivals for foul words.
The US president, who last month called Sondland "a really good man", told reporters on Wednesday that "I don't know him very well."
Among the revelations Wednesday in the impeachment inquiry into Donald Trump, an ambassador revealed how he employs profanity-laden 'Trump-speak' in hopes of relating to the US president.
In an unusual moment of levity in the televised hearing, Gordon Sondland, the US ambassador to the European Union, acknowledged he may have told Trump that Ukraine's leader "loves your ass."
"That sounds like something I would say," Sondland, a hotel owner who received the ambassadorship after donating to Trump, said with a smile when asked by the Democratic counsel about the account.
"That's how President Trump and I communicate, a lot of four-letter words. In this case, three-letter," he said, drawing laughter from the crowd.
Sondland said he was trying to explain to Trump how Ukraine's new president, Volodymyr Zelensky, was "very willing to work with the United States and was being very amicable."
"So putting it in Trump-speak -- by saying 'he loves your ass, he'll do whatever you want' -- meant that he would really work with us on a whole host of issues," Sondland said.