The most common and most likely answer to this crossword clue is the 8 letter word HUMBLING
I've seen this crossword clue in The Daily Telegraph
H
U
M
B
L
I
N
G
Buddy explains!

The straight part
We know that "Lowering" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lowering = humbling.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 HUMBLING mean?
HUMBLING verb- To defeat or reduce the power, independence, or pride of
- To make humble or lowly; to make less proud or arrogant; to make meek and submissive.
- An event which causes humbleness; a set-down.
- Of higher rank, status, quality, strength, etc.; inducing a feeling of inferiority.
- Of an animal: to remove the horns; to poll.
- To separate (barley, oats, etc.) from the awns.