CJK Unified Ideograph-55Db

It depends on the reading and the words around it. The earliest explicit explanation found is the Eastern Han Shuowen Jiezi: 嗛 is "what the mouth holds," with 口 for meaning and 兼 for sound.

That is the character's original job: writing xián, holding something in the mouth. Later classical sources stretch one shape across several jobs: Shiji uses xián for carrying food and for harbouring a grudge; the Guliang tradition uses qiàn for a failed grain crop; other lexicons record qiān humility, qiè satisfaction, and qiǎn an animal's cheek pouch.

The connections are documented, not guesswork: the mouth sense is the same word as 銜, while the humility, satisfaction, and shortage senses are alternate written forms of 謙, 慊, and 歉. Neighbouring words pick the reading: 嗛嗛之德 is humble virtue, while 嗛而未發 is a grudge held back unspoken. Its computer encoding is only a catalogue record.

What does 嗛 mean in a message?

Treat it as a quotation, not a reaction. A lone 嗛 names no reading by itself; the surrounding line or a Hakka-language setting does. In ordinary modern Mandarin, write the common counterpart for hold, grudge, humble, shortage, or satisfied instead.

Using 嗛 marks the text as bookish: a classical quote, a dictionary thread, or a dialect spelling. Do not force it into small talk.