Oddball and Rare bird

Oddball noun - A person of odd or whimsical habits.

Rare bird and oddball are semantically related In some cases you can use "Rare bird" instead a noun "Oddball".

Rare bird noun - A rare or unique person.

Oddball and rare bird are semantically related in odd person topic. You can use "Oddball" instead a noun phrase "Rare bird".