noun
mole; whistle-blower; informant; betrayer
Refers to someone who secretly passes inside information to an opposing party, often in espionage, organizations, or criminal contexts.
警察は組織に内通者がいることを突き止めた。
The police discovered that there was a mole inside the organization.
彼は会社の不正を内部告発した内通者だ。
He is a whistle-blower who exposed the company's wrongdoing.
noun
Rare, old-fashioned use for someone who commits adultery. Modern Japanese typically uses 不倫相手 or 浮気相手.
古い小説では、内通者という言葉が不倫の相手を指すことがある。
In old novels, the word 内通者 can refer to an adulterous partner.
密告者 is an informant who reports to authorities, often with a nuance of tattling; 内通者 implies secret communication with an opposing side.
Compound of 内通 (secret communication) + 者 (person). The exact historical derivation is uncertain.