Support for climbers still shaking, holding on (7)
I believe the answer is:
trellis
'support for climbers' is the definition.
(I've seen this before)
'still shaking holding on' is the wordplay.
'shaking' is an anagram indicator.
'holding' means one lot of letters goes inside another.
'on' becomes 're' ('on' can be mean 'with reference to').
'still' with letters rearranged gives 'tllis'.
'tllis' placed around 're' is 'TRELLIS'.
(Other definitions for trellis that I've seen before include "Light framework for climbing plants" , "Support for creepers" , "Garden framework for climbers" , "Garden climbing frame" , "Plant-training lattice" .)