Sticking together, which is understandable (8)
I believe the answer is:
coherent
I believe this is a double definition.
'sticking together' is the first definition.
(I've seen this before)
'understandable' is the second definition.
(I've seen this in another clue)
'which is' acts as a link.
(Other definitions for coherent that I've seen before include "Not rambling in speech or reasoning" , "Able to speak logically" , "Logical and lucid" , "Meaningful" , "Intelligible and lucid" .)