Reducer and Reduction gear

Reducer noun - A substance capable of bringing about the reduction of another substance as it itself is oxidized; used in photography to lessen the density of a negative or print by oxidizing some of the loose silver.

Reduction gear and reducer are semantically related in gear mechanism topic. In some cases you can use "Reduction gear" instead a noun "Reducer", when it comes to topics like gearbox, gear box.

Reduction gear noun - Gearing that reduces an input speed to a slower output speed.

Reducer and reduction gear are semantically related in gear mechanism topic. You can use "Reducer" instead a noun phrase "Reduction gear", if it concerns topics such as gearbox, gear box.