beard, mustache
髥 centers on facial hair: a beard or mustache. The meanings are closely related, both referring to hair growing on the lower face.
髥 combines 髟 (hair) with 冄, which likely contributes a phonetic element. The character is used specifically for facial hair.
The top 髟 means hair, and the bottom 冄 looks like a flowing beard. Picture long hair on the head and a thick beard below.
For ゼン, imagine a Zen master with a long, flowing beard meditating peacefully: Zen -> ゼン.