yǎn​xiàn

informer

眼线 眼線 yǎn​xiàn
informer noun
A person who is planted to secretly scout or gather information, such as a spy, scout, or snitch

I'm her eyes and ears on the outside.

eyeliner
Makeup applied in a line along the edge of the eyelid

Frequency

Movie subtitles
2.50 per million appears in 1% of films
Written text
6.15 per million

Sources