The most common and most likely answer to this crossword clue is the 8 letter word BRANDISH
I've seen this crossword clue in Financial Times
B
R
A
N
D
I
S
H
More clues leading to the result BRANDISH
Buddy explains!

The straight part
We know that "Shake" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shake = brandish.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 BRANDISH mean?
BRANDISH noun- The act of flourishing or waving.
- To move or swing a weapon back and forth, particularly if demonstrating anger, threat or skill.
- To bear something with ostentatious show.