The Collaborative International Dictionary of English v.0.48:

Deviltry \Dev"il*try\, n.; pl. Deviltries.
   Diabolical conduct; malignant mischief; devilry. --C. Reade.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deviltry
    n 1: wicked and cruel behavior [syn: deviltry, devilry]
    2: reckless or malicious behavior that causes discomfort or
       annoyance in others [syn: mischief, mischief-making,
       mischievousness, deviltry, devilry, devilment,
       rascality, roguery, roguishness, shenanigan]