Tremble from fear (7)
I believe the answer is:
shudder
'tremble from fear' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for shudder that I've seen before include "Shiver in fear or revulsion" , "Shake convulsively" , "Vibration" , "Convulsion" , "Shiver with horror" .)