The branch is a symbol of peace (5)
I believe the answer is:
olive
'the branch is a symbol of peace' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for olive that I've seen before include "Oil-producing fruit" , "Fruit, source of oil" , "Greyish-green colour" , "A Med. fruit-tree" , "Yellowy-green colour and fruit" .)