Take away something vital, say (7)
I believe the answer is:
deliver
'say' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for deliver that I've seen before include "Carry < , and give birth to" , "Bring to a destination and hand over" , "what the errand boy does" , "Bring (letters, etc)" , "bear" .)