The Collaborative International Dictionary of English v.0.48:

Peccadillo \Pec`ca*dil"lo\, n.; pl. Peccadillos. [Sp.
   pecadillo, dim. of pecado a sin, fr. L. peccatum. See
   Peccant.]
   A slight trespass or offense; a petty crime; a trifling
   fault. --Sir W. Scott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

peccadillo
    n 1: a petty misdeed [syn: indiscretion, peccadillo]