Wiktionary
microgenia
n. (context medicine English) The presence of an unusually small or deformed chin.
Wikipedia
Microgenia
Microgenia is the medical term for an unusually small or deformed chin.
The contrasting condition, an enlarged chin, is called "macrogenia".
Microgenia (gastropod)
Microgenia is a genus of sea snails, marine gastropod mollusks in the family Raphitomidae.