peccadillo, noun, a very minor or slight sin or offense; a trifling fault
The plural form is either peccadilloes or peccadillos. Most sources say the first known use was 1585-1595, but the excerpt from the book below is from the much earlier year of 1405.
From the Spanish pecadillo, a diminutive of pecado "sin." Pecado is in turn from the Latin peccatum "transgression."
Sarah was willing to overlook her husband's peccadilloes.
Most people see speeding on the highway as only a peccadillo.
From The Book of the City of Ladies by Christine de Pizan:
"But, just as I told you before, the fool sees his neighbor's peccadillo and fails to see his own enormous crime."