Part of karabiner that’s not moving (5)
I believe the answer is:
inert
'not moving' is the definition.
(I've seen this before)
'part of karabiner that's' is the wordplay.
'part of' indicates a hidden word.
'INERT' is hidden within 'karabiner that'.
(Other definitions for inert that I've seen before include "Like e.g. xenon" , "Lifeless; apathetic" , "Inter, being unable to move" , "Unreacting" , "Without the strength to move" .)