discontented, sad, gloomy
欿 centers on a heavy, dissatisfied emotional state: feeling discontented, sad, or gloomy. The meanings all point to a low, unsettled mood.
欿 combines 臽 (a pit or trap) with 欠 (a person with mouth open, often associated with lack or deficiency). The idea of a pit or hollow combined with lack suggests a sunken, discontented state. The exact historical development is uncertain.
A person (欠) falling into a pit (臽) feels trapped and gloomy. The pit represents a low point, and the open-mouthed person shows discontent.
For タン, imagine a discontented person sighing with a heavy 'tan' sound, like a dull thud. The 'tan' echoes the gloomy mood.