One at a hen party? (4)
I believe the answer is:
bird
This clue might be a double definition.
'one' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'a hen party?' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'at' acts as a link.
Can you help me to learn more?
(Other definitions for bird that I've seen before include "Nest builder?" , "Member of class Aves" , "Prison sentence - hawk, perhaps" , "Creature - time in prison" , "Feathered creature" .)