A figure of speech in which a part stands for the whole. Such as:
Classification of a noun standing for the noun itself:
vessel for ship
weapon for sword
creature for man
arms for rifles
Noun standing for the classification:
bread for food
cutthroat for assassin
Part substituted for the whole:
sail for ship
hands for helpers
roofs for houses
Noun itself used for what is derived from it:
silver for money
canvas for sail
steel for sword