Board Thread:Questions and Answers/@comment-88.199.132.125-20151017193250/@comment-5014364-20151018002745

While it is vague, "massive" is more than "heavy".

It is relative to the initial size of the army: if an army starts with 100,000 and loses 1,000 in a battle, the losses are minor (unless described as relatively heavy in that context for some reason)....if an army starts with 2,000 men, and loses 1,000 in a battle, then those are indeed heavy loses in that context.

Loosely I'd consider a loss of over half to be beyond "heavy" and into "massive" - really only use "massive" to describe when an entire army group gets wiped out.