False friend 假朋友 / 偽りの友
jiǎ péngyǒu / itsuwari no tomo · from English (from French faux amis)
What is a false friend?
A false friend looks or sounds like a word in another language but means something different, like Japanese 手紙 (letter) vs Chinese 手紙 (toilet paper).
False friends are frequent between Chinese, Japanese and Korean because they share Sino-derived vocabulary that drifted in meaning. Loanwords such as Japanese マンション create false friends with English too. They are a top source of memorable mistakes.
Examples
手紙 tegami (Japanese: letter) vs 手紙 shǒuzhǐ (Chinese: toilet paper); 勉強 benkyō (Japanese: study) vs miǎnqiǎng (Chinese: reluctantly); マンション manshon (apartment, not mansion); 愛人 àirén (spouse in mainland usage) vs aijin (Japanese: lover)
Kungfucius says: Write a letter in Japanese, hand it to a Chinese friend, and you have just given them toilet paper.