The capacity to act, and the cost of acting — a thing this house budgets honestly, in vessels and in windows alike.
Greek energeia (activity, operation), en- (in) plus ergon (work); the capacity for work held within a thing.
Its root is work held inside something before it is spent: ergon is the same root behind synergy and ergonomic. Energy is that stored capacity for work, which is why it can be budgeted honestly, a thing with a fixed store of work in it has an edge somewhere, even before anyone finds it.