Monster ran out: I'm shaking! (8)
I believe the answer is:
minotaur
'monster' is the definition.
(I know that Minotaur is a type of mythical monster)
'ran out i'm shaking' is the wordplay.
'shaking' indicates anagramming the letters.
'ran'+'out'+'im'='ranoutim'
'ranoutim' with letters rearranged gives 'MINOTAUR'.
(Other definitions for minotaur that I've seen before include "Cretan labyrinth resident" , "Bull-headed type" , "Mythical bull-headed monster" , "Mythical creature" , "In Greek myth, the bull-man monster slain by Theseus in the labyrinth in Crete" .)