Synecdoche

Part of speech: noun (n.)

A figure or trope by which a part of a thing is put for the whole (as, fifty sail for fifty ships), or the whole for a part (as, the smiling year for spring), the species for the genus (as, cutthroat for assassin), the genus for the species (as, a creature for a man), the name of the material for the thing made, etc. Bain.