Astounded by a commercial about a labyrinth (6)
I believe the answer is:
amazed
'astounded' is the definition.
(I know that astounded can be written as amazed)
'a commercial about a labyrinth' is the wordplay.
'a commercial' becomes 'ad' (abbreviation for advertisement).
'about' means one lot of letters goes inside another.
'a labyrinth' becomes 'maze' (synonyms).
'ad' enclosing 'maze' is 'AMAZED'.
'by' acts as a link.
(Other definitions for amazed that I've seen before include "Astonished, stunned" , "Greatly surprised, never would have thought it" , "knocked for six" , "was stunning" , "Completely surprised" .)