The most common and most likely answer to this crossword clue is the 9 letter word DIFFUSION
D
I
F
F
U
S
I
O
N
Buddy explains!
The straight part
We know that "spreading" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spreading = diffusion.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 DIFFUSION mean?
DIFFUSION noun- The act of diffusing or dispersing something, or the property of being diffused or dispersed; dispersion.
- The scattering of light by reflection from a rough surface, or by passage through a translucent medium.
- The intermingling of the molecules of a fluid due to random thermal agitation.
- The spread of cultural or linguistic practices, or social institutions, in one or more communities.
- The gradual spread and adoption of goods or services.
- Exchange of airborne media between regions in space in an apparently random motion of a small scale.
- The movement of water vapor from regions of high concentration (high water vapor pressure) toward regions of lower concentration.