King and fool join together (4)
I believe the answer is:
knit
'join together' is the definition.
(I've seen this before)
'king and fool' is the wordplay.
'king' becomes 'k'.
'and' means one lot of letters go next to another.
'fool' becomes 'nit' (I've seen this before).
'k'+'nit'='KNIT'
(Other definitions for knit that I've seen before include "Work with wool and needles" , "Make a sweater, maybe" , "Use needles and wool" , "Unite; work wool" , "Make woollen objects" .)