Source : Webster's Revised Unabridged Dictionary (1913)

Amateurish \Am`a*teur"ish\, a.
   In the style of an amateur; superficial or defective like the
   work of an amateur. -- {Am`a*teur"ish*ly}, adv. --
   {Am`a*teur"ish*ness}, n.

Source : WordNet®

amateurishly
     adv : in an amateurish manner; "he performed the piece
           amateurishly" [syn: {like an amateur}] [ant: {expertly}]