Unsymmetrical dimethlyhydrazine or "UDMH" is a propellant which has been used by Russian, American, European, Chinese, and Indian rockets.
Russian rocket engineers nickname it "heptyl". Why was this name chosen, especially when it means a compound with 7 carbon atoms, and UDMH has only two?
Addendum: As several commenters also seem to believe, my suspicion is that the name was chosen as a codeword during the Cold War to deceive enemies. However, that is merely a guess, which I why I originally asked
(Support your answer with sources; no speculation please.)
The article cited by Wikipedia states only
To be specific, the Proton-M — a booster rocket used for decades to carry commercial and military payloads — relies on a combination of unsymmetrical dimethylhydrazine (better known as heptyl fuel) and nitrogen tetroxide.
without providing any source for that claim, and no reason why that name was chosen.