peccadillo

pec·ca·dil·lo  [pek-uh-dil-oh] 

noun, plural pec·ca·dil·loes, pec·ca·dil·los.

a very minor or slight sin or offense; a trifling fault.

Origin: 

1585–95;  < Spanish pecadillo,  diminutive of pecado  sin < Latin peccātum  transgression, noun use of neuter of past participle of peccāre  to err, offend

Synonyms 

lapse, slip, faux pas, indiscretion.