what's the difference betwen synecdoche and netonymy,i can not figure out, i think they are the same.
synecdoche is when part of the name of something is used to represent the whole name. This is common in sport, when instead of saying "Liverpool Tigers", the commentator says, "Liverpool is one goal up so far in the match." Liverpool the city is not - it is the team, Liverpool Tigers which has scored the extra goal.
metonymy is when we substitute the name of an attribute of what we are referring to, for the actual thing meant.
Let me give you an example. In the place where I used to work, we dressed relatively casually, in sports coats. However, the men in the very senior administrative positions at the hospital would all wear business suits every day.
When we then referred to these people, we didn't say, the administrators, or, the board of the hospital, but called them, "the suits". "Suits" is not part of their name (see synecdoche), but some atrribute about them - they always wear suits. It's entomological source is from a word meaning "change of name".