Actress Scarlett Johansson and her husband Colin Jost have revealed the naming technique for their son.
They told Entertainment Tonight they thought the naming technique had led to a "charming" moniker that met with the approval of all their friends - but not her mother-in-law, reports femalefirst.co.uk.
She said: "We just threw a bunch of letters together. I just really thought it was charming and our friends liked it."
Admitting her mum-in-law was not so fond of the name, she said: "Colin's mom had a little bit of a harder time with it. She kept suggesting other versions of it for a while. I was like, 'He's already here. He's out. Like, it's past that time'."
Scarlett and Colin, who married in 2020, announced the arrival of their son in April 2021.
Colin has also told how his mum "didn't quite understand" their choice for their son's name.
He said: "After three or four days, she would be like, 'Cosmo? Is it final? Did you submit the birth certificate'?"
"We were like, 'Oh yeah, we did that at the hospital'. 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.
Maybe you call him Cosimo, that's his real name, and then you could call him still Cosmo?'"
The comic added it was only after his mum consulted others she gave the name her approval.
He added: "She lives in Staten Island. Eventually she started meeting various members of the Italian community who have a lot of Cosmo relatives.
"And so then she would call and she would say, 'I met someone. They said their uncle's name is Cosmo, so it is OK'.
"Then she goes, 'There's also a patron saint called Cosmos, so that's another option'."
But he added he told her "we don't need more options (or) worse variants on Cosmo!, thanks, mom".