beard, mustache
髯 centers on facial hair: a beard or mustache. The two meanings are closely related as types of hair growing on the lower face.
髯 combines 髟 (hair) with 冉, which likely contributes the sound and may be a remnant of an older phonetic component. The character specifically denotes facial hair.
The top 髟 is the hair radical, and the bottom 冉 looks like a face with a beard hanging down. Picture long hair growing specifically on the chin and upper lip.
For ゼン, imagine a Zen master with a long flowing beard: Zen -> ゼン, and his beard symbolizes his wisdom.