Severe trial (8)
'severe trial' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ordeal that I've seen before include "Tough test in Laredo" , "Long, unpleasant experience" , "Struggle" , "A difficult or harrowing time" , "Torment" .)
(Another definition for acidtest that I've seen is " It might provide proof".)