Haphazard jolly involving a nationalist party (6)
I believe the answer is:
random
'haphazard' is the definition.
('random' can be similar in meaning to 'haphazard')
'jolly involving a nationalist party' is the wordplay.
'jolly' becomes 'rm'.
'involving' is an insertion indicator.
'nationalist' becomes 'n' (abbreviation in politics).
'party' becomes 'do' (do is a kind of party).
'a'+'n'+'do'='ando'
'rm' enclosing 'ando' is 'RANDOM'.
(Other definitions for random that I've seen before include "Unsystematic" , "can be hit-and-miss" , "Haphazard, with no particular plan" , "Patternless" , "Indiscriminate" .)