Trembling in great rock (7)
I believe the answer is:
granite
'rock' is the definition.
(granite is a kind of rock)
'trembling in great' is the wordplay.
'trembling' is an anagram indicator.
'in'+'great'='ingreat'
'ingreat' is an anagram of 'GRANITE'.
(Other definitions for granite that I've seen before include "Igneous rock, generally composed of feldspar and mica and quartz" , "A very hard rock from Tangier" , "Tearing (anag.)" , "Crystalline rock" , "Resilience; stone" .)