President Biden expressed regret on Saturday for using the word “illegal” to describe an undocumented immigrant who has been charged in the killing of a 22-year-old nursing student in Georgia, agreeing with his progressive critics that it was an inappropriate term.

Mr. Biden used the word during an unscripted colloquy with Republicans during his State of the Union address on Thursday night, and then came under fire from immigration supporters who consider the term dehumanizing. Among those who said he should not have used it were several congressional Democrats.

“I shouldn’t have used ‘illegal’; it’s ‘undocumented,’” Mr. Biden said on Saturday in an interview with Jonathan Capehart on MSNBC, during which he addressed his disagreements with former President Donald J. Trump.

“And look, when I spoke about the difference between Trump and me, one of the things I talked about in the border was his, the way he talks about ‘vermin,’ the way he talks about these people ‘polluting the blood,’ ” he said, adding, “I talked about what I’m not going to do. What I won’t do. I’m not going to treat any, any, any of these people with disrespect.”

He continued: “Look, they built the country. The reason our economy is growing. We have to control the border and more orderly flow, but I don’t share his view at all.”

Mr. Capehart asked if that meant he regretted using the word “illegal.”

“Yes,” Mr. Biden answered.

The president’s reply went further than when he was first asked about the matter by reporters on Friday. He did not explicitly take back the term at that point, noting that the immigrant charged in the murder in Georgia was “technically not supposed to be here.”