From Dictionary.com:
Dictionary.com Unabridged (v 1.1) - Cite This Source - Share This
Audio Help /ˌpɛkəˈdɪloʊ/ Show Spelled Pronunciation [pek-uh-dil-oh] Show IPA Pronunciation
-noun, plural -loes, -los. a very minor or slight sin or offense; a trifling fault.
A peccadillo is a trifling offense, a small wrong or unimportant sin.