The most common and most likely answer to this crossword clue is the 9 letter word SHRINKAGE
I've seen this crossword clue in Independent
S
H
R
I
N
K
A
G
E
More clues leading to the result SHRINKAGE
- Quiet anger about coloured liquid reduction
- Weight loss, say, from period of psychiatry?
- Quiet anger about tattoo’s reduction in size
- Loss having replaced her gains with investment of a grand
- Doctor takes time to induce contraction
- Reduction of hard bowls area set in green
- Period under psychiatrist revealing loss through theft
- Stock lost from time under psychiatrist
- Loss of stock from years under psychiatrist?
- Wise man accepting hard quantity of ice will show loss of size
Buddy explains!

The straight part
We know that "reduction in size" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reduction in size = shrinkage.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 SHRINKAGE mean?
SHRINKAGE noun- The act of shrinking, or the proportion by which something shrinks.
- The loss of merchandise through theft, spoilage, and obsolescence.
- The reduction in size of the male genitalia when cold, such as from immersion in cold water.