1. A reference to a gross irreverence toward a hallowed or highly respected person, place, or thing: The sacrilegiously inappropriate behavior of the student who was using curse words in class resulted in his being sent to the principal who suspended the boy from school until there was a conference with his parents.
2. Descriptive of treating something holy or important with no respect: Thomas, the archaeologist, was sacrilegiously condemning the slaughter of victims to gods as evidenced by the skeletons he discovered in the ancient ruins.