The most common and most likely answer to this crossword clue is the 10 letter word ULTRASONIC
I've seen this crossword clue in The Guardian
U
L
T
R
A
S
O
N
I
C
More clues leading to the result ULTRASONIC
- Court nails suspect without hearing
- Work on rail cuts – of high frequency
- Radical junior in charge too high to catch?
- Cult’s on-air broadcast not heard by us
- Too high to notice top-class cocaine around a nostril, sadly
- Alto incurs abuse as notes out of range
- Or lunatics can make sounds which are of a frequency too high to be audible
- Like bats or lunatics, raving?
- High-frequency insulator diffused cold
- Court nails criminal, going outside the scope of hearing
Buddy explains!
The straight part
We know that "not heard by us" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not heard by us = ultrasonic.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 ULTRASONIC mean?
ULTRASONIC adjective- (acoustics) Beyond (higher in frequency than) the range of sound perceptible to the human ear; with a frequency of 20 kilohertz or higher.