Dinner party expander (4)
I believe the answer is:
leaf
'dinner party expander' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for leaf that I've seen before include "Bit of tree, of book" , "Sheet of paper" , "Page or piece of foliage" , "Part of a plant and of a book" , "Piece of reading material" .)