The most common and most likely answer to this crossword clue is the 9 letter word VISCOSITY
I've seen this crossword clue in The Guardian
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More clues leading to the result VISCOSITY
Buddy explains!
The straight part
We know that "that makes things sticky" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that makes things sticky = viscosity.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 VISCOSITY mean?
VISCOSITY noun- The state of being viscous.
- A quantity expressing the magnitude of internal friction in a fluid, as measured by the force per unit area resisting uniform flow.
- A tendency to prolong interpersonal encounters.