Not accelerated but immobilised (8)
I believe the answer is:
fastened
'not accelerated' is the definition.
The definition and answer can be both related to change as well as being past participle verbs.
Perhaps you can see a link between them that I can't see?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for fastened that I've seen before include "Secured - buckled" , "Stapled" , "Buttoned, secured" , "Buttoned, tied" .)