Certifiable, so to speak (3)
I believe the answer is:
mad
'certifiable so to speak' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mad that I've seen before include "Idiotic" , "Extremely foolish" , "Crackers" , "like the March Hare" , "(Of a dog) rabid" .)