The most common and most likely answer to this crossword clue is the 12 letter word DISSEMINATED
D
I
S
S
E
M
I
N
A
T
E
D
Buddy explains!

The straight part
We know that "spread" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spread = disseminated.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 DISSEMINATED mean?
DISSEMINATED verb- To sow and scatter principles, ideas, opinions, etc, or concrete things, for growth and propagation, like seeds.
- To become widespread.
- Spread around; widespread
- Spread over a wide area of the body or of an organ