Synecdoche means "the use of the part for the whole," and
metonymy means "the use of something closely related for the
thing actually meant" (Arp 74). Here Thomas uses a synecdoche:

    The hand that signed the paper felled a city;
    Five sovereign fingers taxed the breath,
    Doubled the globe of dead and halved a country...
            (Dylan Thomas, "The Hand That Signed the Paper")

And John Wain a metonymy full of cunning:

    The genuine justifies the genuine:
    A false coin dropped on a stone farmhouse floor
    Is heard as false: but every coiner knows
    This cannot happen on the board room carpet.... (Nims 35)