The phrase "odd one" refers to someone or something that is different or unique compared to others.
Sentences with «odd one»
Took a while to find things in the kitchen as they seemed in odd places. (cambriacoastrentals.com)
The people I know who have tried this diet regard it with a cult like devotion that seems odd for something like a diet. (traditionalcookingschool.com)
Find someone looking for odd jobs and get it done quick. (homelight.com)