adverb, adverb taking the 'to' particle
glancing sharply; giving a sharp look
Describes a quick, sharp, or piercing glance, often with a sense of suspicion or scrutiny. Commonly used with と and verbs like 見る.
彼は私をじろりと見た。
He gave me a sharp glance.
先生が遅刻した生徒をじろりと睨んだ。
The teacher glared sharply at the late student.
Mimetic word; the exact origin is uncertain, but it is likely sound-symbolic, imitating the quick, sharp nature of the glance.