(astronautics) A strap-on booster.

(informal) An artificial phallus attached with a strap, usually a dildo.

(informal, music) Synonym of keytar (“keyboard supported by a strap around the neck and shoulders”).

That can be attached using one or more straps.

(astronautics) Of a booster rocket, that is mounted on the outside of a launch vehicle (typically around the first stage) to provide an additional boost at lift-off, ultimately separating after the first few minutes of ascent.