Meaning of “piercing” - Learner’s Dictionary

piercing

adjective uk us /ˈpɪəsɪŋ/
STRONG

A piercing noise, light, etc is very strong and unpleasant:

I heard a loud, piercing scream.
EYES

Piercing eyes seem to look at you very closely.

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