Sloth? One near it, trembling (7)
I believe the answer is:
inertia
'sloth?' is the definition.
(thesaurus)
'one near it trembling' is the wordplay.
'one' becomes 'i' (Roman numeral).
'trembling' indicates anagramming the letters.
'near'+'it'='nearit'
'nearit' with letters rearranged gives 'nertia'.
'i'+'nertia'='INERTIA'
(Other definitions for inertia that I've seen before include "A disposition to remain inactive" , "Way of selling" , "Stagnating state" , "Resistance to motion" , "Disinclination to act" .)