What do you think of the name cyanide ghost as certified codename like solid snake for my spy story?

Answer 1

Generally when you create a code name, it should be something that if you say it in a conversation it is not going to attract attention.  The phrase "cyanide ghost" is going to stand out.  Someone passing by and hearing it could be drawn into to listen to the conversation.  

You would probably want to go with a more common phrase,  (That would also rule out "soild snake" as a code name.)

Answer 2

It's hard to care when you've already asked this question a million and one times...