leer (v.)

1520s, "to look obliquely" (since 18c. usually implying a lustful, wolfish, malicious intent), probably from Middle English noun ler "cheek," from Old English hleor "the cheek, the face," from Proto-Germanic *hleuza- "near the ear," from *hleuso- "ear," from PIE root *kleu- "to hear." If so, the notion is probably of "looking askance" (compare the figurative development of cheek). Related: Leered; leering.

"a significant glance, amorous or malign or both," 1590s, from leer (v.).