Antonyms of adj impeccable

2 senses of impeccable

Sense 1
faultless, immaculate, impeccable -- (without fault or error; "faultless logic"; "speaks impeccable French"; "timing and technique were immaculate"; "an immaculate record")

INDIRECT (VIA perfect) -> imperfect -- (not perfect; defective or inadequate; "had only an imperfect understanding of his responsibilities"; "imperfect mortals"; "drainage here is imperfect")

Sense 2
impeccable -- (not capable of sin)

INDIRECT (VIA virtuous) -> wicked -- (morally bad in principle or practice)

Similarity of adj impeccable

2 senses of impeccable

Sense 1
faultless, immaculate, impeccable -- (without fault or error; "faultless logic"; "speaks impeccable French"; "timing and technique were immaculate"; "an immaculate record")
       => perfect (vs. imperfect) -- (being complete of its kind and without defect or blemish; "a perfect circle"; "a perfect reproduction"; "perfect happiness"; "perfect manners"; "a perfect specimen"; "a perfect day")

Sense 2
impeccable -- (not capable of sin)
       => virtuous (vs. wicked) -- (morally excellent)