Chin

A chin was part of humanoid anatomy.

The Eleventh Doctor was remarked often for having a slightly large one, which got himself nicknamed (ironically by his previous self) "Chinny". (TV: The Day of the Doctor) Oswin Oswald said he could put an eye out with it, and called him "the chin". (TV: Asylum of the Daleks) The Twelfth Doctor later used the same term to describe his previous incarnation to Bill Potts. (COMIC: The Promise) After the Maitland siblings discovered that the Eleventh Doctor and Clara Oswald were time travellers, Artie Maitland suspected that the Doctor was an alien based on his chin. (TV: The Crimson Horror)

Cassandra O'Brien.Δ17 had her chin completely taken away. (TV: The End of the World)

In non-valid sources
The Tenth Doctor once referred to the Eleventh Doctor as "Chin". (TV: Cinema Introduction)