"My mom, I would say, was slightly thrown by it and didn't quite understand it," Jost, 39, began. "I don't know if she thought it was kind of, like, a hippie thing."
"She would call us ... after three or four days, she'd be like, 'Cosmo. ... And now, is it final? Like, did you submit the birth certificate?'" he continued. "And we're like, 'Oh, yeah, we did that at the hospital.' And she's like, 'OK, interesting. Because I was reading that there's also a name Cosimo with an I, so that could also be an option. She was like, 'Maybe you call him Cosimo -- that's his real name -- but then you can call him still Cosmo.'"
The "A Very Punchable Face" author added that his mom, who lives on Staten Island, then "started meeting various members of the Italian community who have a lot of Cosmo relatives."
"She would call, and she would say, 'I met someone. They said their uncle's name is Cosmo. So it is OK,'" Jost told Meyers.
However, the comedian's mom went on to suggest another variant on her grandson's name.
"I was like, 'It's locked in,'" Jost said. "Then she goes, 'There's also a patron saint called Cosmos, so that's another option.' [I said], 'We don't need more worse options [or] variants on Cosmo. But thanks, Mom.'" Jost's mom was likely referring to Saint Cosmas.
Earlier in the interview, Meyers asked how they came up with the name Cosmo.
"We were just assigned it at the hospital," he quipped. "I think the hospitals now are just so overwhelmed that when the baby comes out, they're just like, 'Oh, that's Frank. Go.'"
In August, Jost confirmed in an Instagram post that he and Johansson had welcomed their first child, writing, "Ok ok we had a baby. His name is Cosmo. We love him very much. Privacy would be greatly appreciated." However, it's unclear when Johansson, 36, gave birth.
Rumors swirled for months that the actress was expecting, but neither of them confirmed the pregnancy until just a few days before Josh revealed they had welcomed their first child. He reportedly dropped the news during a stand-up set at the Ridgefield Playhouse in Connecticut. "We're having a baby, it's exciting," he said, per Page Six.
Cosmo is the first child for the couple, while Johansson shares 7-year-old Rose Dorothy with ex-husband Romain Dauriac.
Jost and Johansson first met when she hosted "Saturday Night Live" back in 2006, and they would see each other periodically over the years. It was when she came back for a cameo appearance during the 2017 finale as Ivanka Trump that the stars finally aligned.
The two got engaged in May 2019 and tied the knot in October 2020.