Meaning of “hollow” - Learner’s Dictionary

hollow

adjective uk us /ˈhɒləʊ/
NOTHING INSIDE

having a hole or empty space inside:

a hollow shell/tube
WITHOUT MEANING

without meaning or real feeling:

a hollow victory
a hollow laugh
hollow cheeks/eyes

If someone has hollow cheeks/eyes, their face seems to curve in around these areas.

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