Quiet dude collapsed, first refusing to tremble (7)
I believe the answer is:
shudder
'to tremble' is the definition.
(I know that shudder is a kind of the tremble)
'quiet dude collapsed first refusing' is the wordplay.
'quiet' becomes 'sh' ('sh' is used to tell someone to be quiet).
'collapsed' indicates an anagram.
'first refusing' becomes 'r' (1st letter of 'refusing').
'dude' with letters rearranged gives 'udde'.
'sh'+'udde'+'r'='SHUDDER'
(Other definitions for shudder that I've seen before include "Vibration" , "Shake convulsively" , "Convulse" , "Shiver in fear or revulsion" , "Shiver; tremble" .)