Like the word "gadzooks" (7)
I believe the answer is:
archaic
'like the word gadzooks' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for archaic that I've seen before include "Antiquated" , "From the past" , "Very old or old-fashioned" , "A long way out of date" , "Belonging to former or ancient times" .)