The most common and most likely answer to this crossword clue is the 6 letter word BELLOW
I've seen this crossword clue in Independent
B
E
L
L
O
W
More clues leading to the result BELLOW
- Live lion's first deep roar
- Loud roar coming from fifty entering underneath
- Novelist left under blankets
- Roar coming from lower down, with twice the heart
- Bill finally penetrating under bark
- Shout in line put in further down
- Sound wanting almost everything expelled from lungs?
- US author not above adding extra line
- Thunder and lightning’s beginning to penetrate lower down
- Thunder and lightning beginning to come in further south
Buddy explains!
The straight part
We know that "booming sound" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case booming sound = bellow.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 BELLOW mean?
BELLOW noun- The deep roar of a large animal, or any similar loud noise.
- To make a loud, deep, hollow noise like the roar of an angry bull.
- To shout in a deep voice.