Yominum sulfide
From Memory Alpha, the free Star Trek reference
Yominum sulfide is a chemical with a molecular formula of K4YM3(SO73ES2).
When Spock was performing a memory test, one of the questions asked him what the molecular formula for yominum sulfide was. (Star Trek IV: The Voyage Home)
Yominium was named after Leonard Nimoy – "Yomin" is "Nimoy" spelled backwards. (Star Trek Encyclopedia)
