Barrier of course due to party lines (4)
I believe the answer is:
doll
'barrier of course' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'party lines' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'lines' becomes 'll' (l is an abbreviation for line).
'do'+'ll'='DOLL'
'due to' is the link.
Can you help me to learn more?
(Other definitions for doll that I've seen before include "Puppet" , "A girl's plaything" , "Toy baby" , "Toy replica of a person" , "Figurine" .)