Unite king and idiot (4)
I believe the answer is:
knit
'unite' is the definition.
(I've seen this before)
'king and idiot' is the wordplay.
'king' becomes 'k'.
'and' means one lot of letters go next to another.
'idiot' becomes 'nit' (I've seen this before).
'k'+'nit'='KNIT'
(Other definitions for knit that I've seen before include "Contract; intertwine" , "Make woollen garments" , "Cause to unite" , "manufacture clothing?" , "Unite; work wool" .)