noun
sharp sidelong glance; glare
A hostile or suspicious look directed sideways, often with the head slightly turned. Conveys anger, distrust, or intimidation.
彼は私に横睨みをくれた。
He gave me a sharp sidelong glare.
上司の横睨みに気づいて、慌てて仕事に戻った。
Noticing my boss's sidelong glare, I hurried back to work.
Compound of 横 (side) and 睨み (glare, from verb 睨む). The exact historical derivation is uncertain, but the meaning is transparent from its components.