synecdoche

noun2

1. •
   (rhetoric) A figure of speech that uses the name of a part of something to represent the whole, or the whole to represent a part, or a specific kind or instance to represent the general category, or the general category to represent a specific kind or instance, or the constituent material to represent the thing made from it.

   • Synecdoche the whole for part will take, Or part for whole, just for the metre's sake. — 1835
2. •
   (rhetoric) The use of this figure of speech.