Synecdoche is a special kind of metonymy in which a thing is names after its part or, vice versa, a part is denoted by the whole thing. It is used to avoid repetition or to enrich poetic imagery. There are three kinds of synecdoches:
A) the pars pro toto synecdoche, in which a an object is called after its part, for example many a day
B) the singularis pro plurali synecdoche, in which a group of people is represented by a single representative, a child is cruel
C) the totum pro parte synecdoche that denotes a part by naming the whole thing, like in my family arrived instead of the members of my family arrived.