Exa Dark Sideræl Musk aka 'Y': What Elon Musk, Grimes’ baby name means

Tesla chief Elon Musk and singer Grimes.

Tesla chief Elon Musk and singer Grimes have welcomed their second baby together and her name is just as unique as their first child’s.

The couple have named their baby daughter Exa Dark Sideræl Musk, Grimes told Vanity Fair. Her older brother is called X Æ A-Xii.

Grimes told the magazine that Exa referred to exaFLOPS --  a supercomputing term. Dark is for the unknown, a “beautiful mystery” of the universe, the magazine reported. Sideræl stands for “the true time of the universe, star time, deep space time”.

Sideræl in the baby’s name also honours Galadriel, Grimes’ favourite character from JRR Tolkien’s masterpiece ‘The Lord of the Rings’, Vanity Fair reported. It is pronounced as “sigh-deer-ee-el”.

Grimes and Elon Musk's daughter, nicknamed Y,  was born through surrogacy in December.

The couple did not publicly announce the child's birth. Instead, it was revealed accidentally when a Vanity Fair reporter was at Grimes' home for an interview and heard the baby crying.

Musk and Grimes' first child had arrived in May 2020 and was named X Æ A-Xii, pronounced “X Ash A 12”.

The boy's name is also replete with science and tech references.

Grimes had elaborated on the child’s name in a tweet after his birth.  “X, the unknown variable, Æ, my elven spelling of Ai (love and/or Artificial intelligence," she had said.

"A", Grimes said, represented "Archangel", which is her favourite song, while "12" was a  tribute to CIA's Lockheed A-12 reconnaissance plane.

Grimes and Elon Musk describe themselves as "semi-separated".

The singer told Vanity Fair that there was no real word for their relationship.

“I would probably refer to him as my boyfriend, but we’re very fluid," Grimes said. "We live in separate houses. We’re best friends. We see each other all the time…. We just have our own thing going on, and I don’t expect other people to understand it.”