The most common and most likely answer to this crossword clue is the 4 plus 4 letter word DUMB SHOW
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More clues leading to the result DUMB SHOW
Buddy explains!

The straight part
We know that "Silent gesture" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case silent gesture = dumb show.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 DUMB SHOW mean?
DUMB SHOW noun- A performance during which the players do not speak; mime.
- The use of gesture in an attempt to convey meaning.