singleton
🇺🇸
/ˈsɪŋɡltən/
🇬🇧
/ˈsɪŋɡltən/
one and only one of something
The singleton in the group was the only one without a pet.
a person who is not married or in a romantic relationship
At 30, she was still a singleton and enjoyed her freedom.
a person or an animal that is not one of a pair
The singleton calf was adopted by the mother cow.