Halting in truck before you finally departed (12)
I believe the answer is:
inarticulate
'halting' is the definition.
(thesaurus)
'in truck before you finally departed' is the wordplay.
'truck' becomes 'artic' (short for articulated lorry).
'before' says to put letters next to each other.
'you' becomes 'u' (commonly used in online communication).
'finally departed' becomes 'late' (late can mean deceased. I am not sure about the 'finally' bit.).
'in'+'artic'+'u'+'late'='INARTICULATE'
(Other definitions for inarticulate that I've seen before include "Unable to express oneself clearly" , "incoherent" , "incapable of clear speech" , "Not clearly expressed" , "hard to understand" .)