Witness Bob dismiss head waiter (8)
I believe the answer is:
observer
'witness bob' is the definition.
'observer' can be an answer for 'witness' (I've seen this before). I'm not sure about the 'bob' bit.
'dismiss head waiter' is the wordplay.
'dismiss head' becomes 'ob' (I can't justify this - if you can you should give a lot more credence to this answer).
'waiter' becomes 'server' (synonyms).
'ob'+'server'='OBSERVER'
Can you help me to learn more?
(Other definitions for observer that I've seen before include "One who watches" , "One watching attentively" , "Viewer" , "Someone watching" , "One keeping his eye on" .)