Gentle contact is accepted by King and son (4)
I believe the answer is:
kiss
'gentle contact' is the definition.
(I've seen this in another clue)
'is accepted by king and son' is the wordplay.
'accepted by' is an insertion indicator (inserted letters are accepted).
'king' becomes 'k' (chess abbreviation).
'and' is a charade indicator (letters next to each other).
'son' becomes 's' (genealogical abbreviation for son).
'k'+'s'='ks'
'is' placed inside 'ks' is 'KISS'.
(Other definitions for kiss that I've seen before include "Smack; peck" , "(Of snooker ball) touch gently; X represents it" , "Act of love" , "Cross" , "Expression of love" .)