The most common and most likely answer to this crossword clue is the 5 letter word BEADY
B
E
A
D
Y
Buddy explains!
The straight part
We know that "looking sinister" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case looking sinister = beady.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BEADY mean?
BEADY adjective- Resembling beads; small, round, and gleaming.
- (of eyes or a look) Bright and penetrating.
- Covered or ornamented with, or as if with, beads.
- Characterized by beads.