One's wartime girlfriend? (5)
I believe the answer is:
popsy
This clue could be a double definition.
'one's' is the first definition.
Both the answer and definition are singular nouns.
Maybe you can see a link between them that I can't see?
'wartime girlfriend?' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Other definitions for popsy that I've seen before include "dish" , "Attractive girl" .)