Source : Webster's Revised Unabridged Dictionary (1913)

Metonymic \Met`o*nym"ic\, Metonymical \Met`o*nym"ic*al\, a. [See
   {Metonymy}.]
   Used by way of metonymy. -- {Met`o*nym"ic*al*ly}, adv.

Source : WordNet®

metonymically
     adv : in a metonymic manner