enjoyment, pleasure
僖 centers on a person's experience of joy: enjoyment and pleasure. It describes a state of happy satisfaction.
僖 combines 亻 (person) with 喜 (joy), suggesting a person experiencing joy or pleasure. The exact historical development is uncertain, but the component structure is clear.
A person 亻 beside 喜 (joy) is someone filled with enjoyment and pleasure.
For キ, imagine a person feeling so much joy they can't help but let out a happy 'key!' sound: key -> キ, and the person 僖 is delighted.