Not seriously uncertain, funding houses (2,3)
I believe the answer is:
in fun
'not seriously' is the definition.
(I've seen this in another clue)
'uncertain funding houses' is the wordplay.
'houses' indicates the answer is hidden within the clue (part of the clue houses the answer).
'IN FUN' is hidden within 'uncertain funding'.
(Other definitions for in fun that I've seen before include "As a joke - not seriously" , "Not intended seriously" , "for a laugh" , "to raise a smile?" .)