rascally

adjective

1. being, characteristic of, or befitting a rascal.

adverb

2. in a rascally manner.

adjective

1. dishonest or mean; base
2. archaic (esp of places) wretchedly unpleasant; miserable

adverb

3. in a dishonest or mean fashion

adj.

“low, mean, unprincipled,” from rascal + -ly (1).