Greeting workers with fish (9)
I believe the answer is:
handshake
'greeting' is the definition.
(I've seen this before)
'workers with fish' is the wordplay.
'workers' becomes 'hands' (hand is a kind of worker).
'with' means one lot of letters go next to another.
'fish' becomes 'hake' (hake is a kind of fish).
'hands'+'hake'='HANDSHAKE'
(Other definitions for handshake that I've seen before include "Gesture of greeting or of agreeing a deal" , "Physical greeting" , "introductory offer?" , "acknowledgment" , "Conventional sort of manual greeting" .)