The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

amateurishness \amateurishness\ n.
   Behavior that demonstrates a lack of professional competency.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

amateurishness
    n 1: something that demonstrates a lack of professional
         competency