shade, shelter, protection
庥 centers on providing cover from harm or exposure: shade from the sun, shelter from the elements, or protection in a broader sense.
庥 combines 广 (building or shelter) with 休 (rest), suggesting a place of rest and protection. The exact historical development is uncertain, but the component combination fits the meaning of shade or shelter.
Under a broad roof 广, a person 亻 rests by a tree 木, creating a shaded, sheltered spot. 庥 is that protective shade.
For キュウ, imagine resting in the shade with a cool cucumber (cucumber -> キュウリ) in hand: the first part キュウ of キュウリ cues the reading while you enjoy the shelter.