Seventeen displays a party (5)
I believe the answer is:
event
'a party' is the definition.
'seventeen displays' is the wordplay.
'displays' indicates the answer is hidden within the clue (part of the clue displays the answer).
'EVENT' is hidden within 'seventeen'.
(Other definitions for event that I've seen before include "Something that takes place" , "Particular happening" , "pole vault maybe" , "Meeting" , "long jump, say" .)