Greeting surprises Sikh hosts from behind (4)
I believe the answer is:
kiss
'greeting' is the definition.
(I have seen 'Amorous greeting ' mean 'kiss' so perhaps 'greeting' could also mean 'kiss')
'surprises sikh hosts from behind' is the wordplay.
'hosts' indicates the answer is hidden within the clue.
'from behind' shows that the letters should be reversed in order.
'ssik' can be found hidden inside 'surprises sikh'.
'ssik' in reverse letter order is 'KISS'.
(Other definitions for kiss that I've seen before include "Act of osculation" , "Peck (on cheek or lips?)" , "drop of wax" , "Greet with lips" , "Peck, smacker, X" .)