During an appearance on Conan O'Brien's talk show on Tuesday night, Ashton revealed: "We had another name picked out.
"We got pregnant a couple of weeks after we picked the name but when we were pregnant, the name didn't fit the energy we were feeling. One night, Mila was like, 'This is not the name.' I was like, 'okay it's not the name.'
Ashton Kutcher on Conan
He continued: "I had to get the creative juices going, so we were going to a Lakers game, and I got name tourettes."
Ashton joked: "I just started listing off anything and everything I saw: 'sign, truck, wall, door.' She [was] like, 'Shut up!' I said, 'if you don't accept my bad ideas, you'll never accept the good ones.'
"Then I was like, 'I've got a really dumb idea. What about Wyatt?' She goes, 'That’s it.'
He added: "We gave her the name Isabelle after Mila’s grandfather, who was Yitzhak. And so it has a little heritage."
Ashton Kutcher and Mila Kunis are also engaged to be married
Ashton and Mila's little girl was born on 30 September at Cedars-Sinai Medical Center in Los Angeles. "Mila was born to be a mum," a source told People after.
"She is a kid herself and will be the best mum ever. She will never be a glamour-puss. Their lives will change, but not nearly as drastically as other couples, because they were so ready to be parents and knew what responsibilities they had in store."
The insider added: "Ashton has wanted to be a parent for so long. He is ready to do anything necessary to take care of the baby. He is ecstatic."