Definitions

yǐn to smile at; to sneer at

Etymology

To stretch  the mouth  also provides the pronunciation

About

The Chinese character is a phono-semantic compound, combining the semantic component ('mouth') with the phonetic ('to stretch'), which also provides its pronunciation. Its original meaning, 'to stretch the mouth' (i.e., to smile), is now completely obsolete. Today, the character is used exclusively in the chemical term 吲哚 (yǐnduǒ), a phonetic loan for 'indole', an aromatic heterocyclic organic compound. This repurposing of an archaic character for modern scientific terminology is a common practice.