interstage

noun

1. The structure, generally containing mechanical components and instruments but no engines or fuel tanks, connecting the top of a stage of a multistage rocket to the bottom of the stage above it.
2. The components of a multistage thermonuclear weapon which channel the radiation produced by the primary's fission explosion so as to trigger the implosion of the secondary and ignite a fusion explosion in the secondary's fusion fuel.

adj

1. (not-comparable)Between stages.