Meaning of “sunken” - Learner’s Dictionary

sunken

adjective [ always before noun ] uk us /ˈsʌŋkən/
LOW

at a lower level than the surrounding area:

a sunken bath
SEA

having fallen down to the bottom of the sea:

a sunken ship
sunken eyes/cheeks

eyes or cheeks that make you look sick because they go too far into your face

(Definition of “sunken” from the Cambridge Learner’s Dictionary © Cambridge University Press)