The First Use of Multiverse in Comics?

Notes on "The Multiverse, Part1"

Parallel worlds, counter-Earths, and alternate dimensions have been with us in the comic books almost from the outset. In the world of DC Comics, Wonder Woman encountered a parallel world as far back as 1953 in "Wonder Woman's Invisible Twin" (WW #59), and The Flash famously introduced the concept of Earth-2 and jump-started the DC multiverse with "The Flash of Two Worlds" in 1961 (Flash #123). But when did the phrase "multiverse" first get applied to the infinite number of parallel worlds inhabited by the superhero characters of Marvel and DC?

I imagined the first use of multiverse in the comics would have happened in one of the many Justice League/Justice Society team-ups that took place every year in the pages of The Justice League of America comic book, but reading through these "Crisis" stories didn't turn up any citations. Ditto for any 1960s Superman stories, so chock-full of imaginary tales, doppelgangers, and parallel worlds.

It seems The Multiverse wasn't really popularized until Michael Moorcock started using it in his Elric stories in the 60s and 70s and it took awhile to filter into comic books. The first DC use I can find is Claw the Unconquered #7 (cover-dated May-June 1976), "The People of the Maelstrom", written by David Michelinie and drawn by Ernie Chan. 

Claw #7

Over at Marvel, I couldn't find a reference until What If #10. "What If ... Jane Foster Had Found the Hammer of Thor?", written by Don Glut with art by  Rick Hoburg. The Watcher opines, "But there are infinite parallel worlds in the multiverse ... countless Earths existing in the same space, but in different dimensions."

What If #10