Amazed as lorry roars in front (13)
I believe the answer is:
thunderstruck
'amazed' is the definition.
(synonyms)
'lorry roars in front' is the wordplay.
'lorry' becomes 'truck' (I've seen this before).
'roars' becomes 'thunders' (thundering is a kind of roaring).
'in front' means one lot of letters go next to another.
'truck' put after 'thunders' is 'THUNDERSTRUCK'.
'as' is the link.
(Other definitions for thunderstruck that I've seen before include "Completely taken aback" , "Dumbfounded" , "Very surprised, shocked" , "Extremely surprised" , "Flabbergasted" .)