bus
n.— «One of the most complicated parts of the process involves miniaturising a nuclear device so it can fit on a missile.…The process involves fitting to a missile what is called a “bus” on which the warheads sit, covered by a cone, said Dr Lee Willett, a defence analyst at the Royal United Services Institute.» —“N Korea still short of nuclear goal” by Penny Spiller BBC Oct. 9, 2006. (source: Double-Tongued Dictionary)