Hypothetically, the irony is lost (2,6)
I believe the answer is:
in theory
'hypothetically' is the definition.
(I've seen this in another clue)
'the irony is lost' is the wordplay.
'is lost' indicates anagramming the letters.
'the'+'irony'='theirony'
'theirony' with letters rearranged gives 'IN THEORY'.
(Other definitions for in theory that I've seen before include "In principal" , "On paper" , "according to the assumed facts" , "Ideally" .)