The crossword solutions for the term 'up to no good' are SINISTER (8 letters) and EVIL (4 letters). SINISTER is an adjective that means having or showing a desire to do EVIL. It is often used to describe someone's intentions or behavior. EVIL is also an adjective that means morally wrong or bad. It is often used to describe someone's actions or intentions. Both words can be used to describe someone who is up to no good.