Head server removed fish in French restaurant perhaps, because it might make people sick (6)
I believe the answer is:
poison
'head' is the definition.
The definition and answer can be both to do with social activities as well as being verbs in their base form.
Maybe you can see an association between them that I don't see?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for poison that I've seen before include "If taken, it can harm or kill" , "I spoon up the lethal substance" , "Damaging stuff - drink?" , "Dangerous substance" , "Substance that damages tissues or causes death" .)