Chou Collection, Upper Volume
Radical: Mouth (kǒu)
Character: pin
Kangxi Strokes: 19
Page 213, Entry 35
Guangyun: Pronounced pin
Jiyun, Yunhui, Zhengyun: Pronounced pin
Sound: yin
Zhengzitong: The appearance of knitting the brows.
Comprehensive Mirror for Aid in Government (Zizhitongjian): Han Zhaohou said: A wise ruler is frugal with even a single frown or smile.
Wang Yun poem: Withheld smile, slight frown moving.
Also, Zhengzitong states it is a variant form of pin.
Luo Binwang poem: The water chestnut flower on the vanity mirror is dimmed, the willow-leaf eyebrows are frowned.
Also, it is a variant form of pin.
Zhuangzi, Heaven's Operation chapter: Xi Shi had a heart ailment and frowned.
Commentary: To knit the brows is called pin.
Li Bai poem: One cannot be jealous of moth-like eyebrows, how much less so by imitating their frown.
Also, it is used interchangeably with pin.
Mencius: Already frowning and furrowing the brows, he said.
Wang Chong, Balanced Inquiries (Lunheng): The weak wine is sour and bitter, the guest and host both frown in distaste.
Note: According to the Zhengzitong, this character is distinct from the entries under the speech radical. I have never heard of it being interpreted as a smile. If the old commentaries were correct in their claims, then a frown and a smile would be equivalent to saying a smile and a smile, which is difficult to explain in terms of meaning. All the rhyme books that define it as the appearance of a smile are incorrect.