unique
This was his one and only hope.
C'était son seul et unique espoir.
After all, you're my one and only grandchild.
Après tout, tu es mon unique petit-enfant.
— When Marnie Was There (2014)
This is my one and only friend, Lee Jong-su.
Voici mon seul et unique ami, Lee Jong-su.
— Burning (2018)
This was her one and only hope.
C’était son seul et unique espoir.