camp, perform, build, conduct (business)
營 centers on organized human activity: setting up a camp, building something, or conducting business. The idea of performing or carrying out an operation ties these meanings together.
營 is the traditional form of modern 営. It combines 宮 (palace, dwelling) with 火 (fire) and 冖 (cover), suggesting a covered, lit place for organized activity such as a camp or workshop. The exact historical development is uncertain, but the component structure points to a place where work is conducted.
Picture a large tent (冖) with a fire (火) inside and a double-mouthed vessel (吕) at the bottom. This is a camp where people perform tasks, build things, and conduct business around the fire.
For エイ, imagine an 'A'-frame tent in the camp: the letter 'A' sounds like エイ, and the tent is where all the building and business happens.