卧底

Traditional form:

臥底

Pinyin (reading):

wòdǐ

Definitions:

• to hide (as an undercover agent)
• an insider (in a gang of thieves)
• a mole

Characters:

• 卧 - to crouch; to lie down
• 底 - bottom, underside; below, underneath

Traditional characters:

• 臥 - to crouch, to lie down
• 底 - bottom, underside; below, underneath