Synecdoche (提喻）
A figure of speech in which a part is used for the whole, the whole for a part, the specific for the general, the general for the specific, or the material for the thing from which it is made. 一种修辞方法，以局部代表整体（如用手代表水手），以整体代表局部（如用法律代表警官），以特殊代表一般（如用直柄剃刀代表杀人者），以一般代表特殊（如用贼代表扒手），或用原材料代表用该材料制造的东西（如用钢代表剑）
Example: lend me your ears (give me your attention).
He saw some new faces in the classroom.
A fleet of ten sails \ To earn one’s bread \ To count heads
Many hands provide great strength.
The poor man had twelve mouths to feed.
Lend me your ears. ( give me your attention.)
Metonymy（借代）换喻，转喻：
A figure of speech in which one word or phrase is substituted for another with which it is closely associated, as in the use of “ Washington” for “the United States government” or of “the sword” for “military power”.
一种一个词或词组被另一个与之有紧密联系的词或词组替换的修辞方法，如用华盛顿代替美政府或用剑代替军事力量
Example:bowing to the sceptered isle. (Great Britain)
Young people should have more respect for gray hairs. (old people)
The kettle is boiling. (water in the kettle)
He took to the bottle.他爱上了喝酒。(wine in the bottle)
I’m reading Lu Xun. ( Lu Xun’s works)
He’s listening to Beethoven. (Beethoven’s works)
He is booked out for the whole season.他这个季演出的票全订出去了。(the tickets for his concerts)
When she entered high school, she would wear a wardrobe that no one else would be able to match.当她上中学时，她所穿的衣服任何一个人都没法比。
They will resort to the sword if the negotiation does no work.
She is the first violin in the band.她是乐队中的第一小提琴手。
Both are figures of speech used in rhetoric. They’re not the same thing, though metonymy is often interpreted so widely that synecdoche can be regarded as a special case of it.
As for Synecdoche, You use this when you speak of a part of something but mean the whole thing. When Patrick O’Brian has Captain Jack Aubrey tell his first lieutenant（陆军中尉）to “let the hands go to dinner” he’s employing synecdoche
