The most common and most likely answer to this crossword clue is the 4 letter word DUMB
I've seen this crossword clue in The Daily Telegraph
D
U
M
B
More clues leading to the result DUMB
- Tailless flying elephant? I’m speechless
- Stupid name, admits head of marketing
- Stupid clanger? It’s raised in gym
- Mum married in style
- Silent call — a number’s engaged
- Bimbo not entirely in possession of bodybuilder
- Regulars in dour mob lacking intelligence
- Silent animated Disney film, unfinished
- Struck thus, one can’t speak
- Stupid call to get married
Buddy explains!

The straight part
We know that "Silent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case silent = dumb.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 mean?
DUMB adjective- Unable to speak; lacking power of speech (kept in "deaf, dumb, and blind").
- Silent; unaccompanied by words.
- (especially of a person) Extremely stupid.
- Pointless, foolish, lacking intellectual content or value.
- Lacking brightness or clearness, as a colour.
- To silence.
- To make stupid.
- To represent as stupid.
- To reduce the intellectual demands of.