long hair
髧 centers on long hair, specifically hair that hangs down or drapes. It describes the visual quality of lengthy, flowing hair.
髧 combines the hair radical 髟 with the phonetic component 冘, which likely contributed the sound. The character is used to describe long, hanging hair.
The top part 髟 represents hair, and the bottom part 冘 looks like a person with long hair flowing down. Picture someone with hair so long it drapes over their shoulders.
For タン, imagine a long-haired person getting a tan while their hair hangs down: tan -> タン, and the long hair flows in the sun.