Reserves and Reenforcement

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

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

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. Sometimes you can use "Reserves" instead a noun "Reenforcement".