metonym = the name of one thing used to represent another of which it is an attribute or with which it is associated

Referring to the "Crown" to mean the kingdom and all it encompasses, is to use a metonym.

euphemism = substitution of an agreeable or inoffensive expression for one that may offend or suggest something unpleasant

We often say "passed on" as a euphemism for "died."

dysphemism = the substitution of a disagreeable, offensive, or disparaging expression for an agreeable or inoffensive one

"Idiot box" is a frequent dysphemism for "television."

eponym = one for whom or which something is or is believed to be named

"Diesel engine" is the eponym for the internal combustion engine invented by Rudolph Diesel.