Another question is euphemism more similar to irony than it is to double entendre? I think it is in that both involve substitution. How do they differ then? Is the substituted word/phrase in irony necessarily opposite to the real meaning; while in euphemism there is a slight extension of meaning. I think euphemism is similar to DE only in that DE is complete extension while euphemism is part substitution and part extension.
PS: is a raven like a writing desk?