What device can be implemented in an engine's design to reduce the forward speed of an aircraft?

The thrust reverser is a vital component designed specifically for reducing the forward speed of an aircraft during landing, and it achieves this by reversing the direction of the engine's thrust. When deployed, the thrust reverser directs the exhaust flow forward, rather than backward, which creates opposing force to the aircraft's motion. This additional braking effect significantly shortens landing distances and improves safety during landing operations.

In contrast, while the flap system may help increase lift at lower speeds and can contribute to better control during landing, it does not actively reduce the aircraft's forward speed. Speed brakes serve a similar purpose by creating drag to slow the aircraft down, but they are separate from the thrust reversal system. Landing gear is primarily for supporting the aircraft on the ground and does not play a role in speed reduction during flight. Thus, the thrust reverser is the most effective device for this specific purpose in an engine's design.