Reenforcement and Reserves

Reenforcement noun - A military operation (often involving new supplies of men and materiel) to strengthen a military force or aid in the performance of its mission.

Reserves and reenforcement are semantically related. In some cases you can use "Reserves" instead a noun "Reenforcement".

Reserves noun - Civilians trained as soldiers but not part of the regular army.

Reenforcement and reserves are semantically related. Sometimes you can replace term "Reenforcement" with "Reserves", this nouns are similar.