It does not "need" the word concubine. However, you asked the question:
Which I took to mean "if the only difference is the inheritences given in your will, why would you assign different inheritences to women, that would flow-on to their children, and how could that be biblical?". So I presented a very realistic modern example of two women with very different inheritance rights from the same man.
I am not talking about deliberately taking a dodgy woman. I am talking about the situation where a man with a long-standing wife (say 20 years), whom he has built a family and business with, takes on a new wife who has not contributed to their assets. Although he has chosen her carefully, expects her to stick around, and would not have married her otherwise, he does recognise she has had a difficult background and he cannot predict the future - he also knows that polygamy is hard work and has risks. So for the protection of wife 1 and her children in a worst-case scenario he explicitly wills the assets that wife 1 helped create to her (and their children by extension), and only gives wife 2 a stake in assets relating directly to her or acquired by the family after she arrived.
Incidentally, that scenario is actually based on New Zealand inheritence law, which explicitly gives two women both in relationships with a man disproportionate rights to his assets depending on the length of their relationships and their personal contributions to those assets. I have deliberately aligned the scenario with secular law for reasons that will become clear below.
Can I pare back past the emotion please, and ask three simple questions about this practical scenario.
- Assuming they are called "wife 1" and "wife 2", not even a hint of the word "concubine" anywhere, could this unequal treatment of the wives in the man's will be considered reasonable? (not claiming it's perfect, I don't want to debate minutae, the question is "could it be considered reasonable?").
- Now let us call these same two women "wife" and "de-facto partner", as they are viewed in secular law. Let us assume that the marriage contract itself that "wife" has, and the time she has been married to her husband, automatically entitles her to the asset split above. And the "de-facto partner" also automatically receives the above split in assets due purely to the fact that she entered into the family later. The same inheritance split applies, but is now automatic due entirely to their legal and practical statuses as "wife of 20 years" and "new de-facto partner". Can this automatic unequal treatment of "wife" and "partner" under the law be considered reasonable?
- Now let us assume this exact same family is living in ancient Israel. Wife is called "wife", partner is called "concubine". But the exact same inheritance split has been assigned to the two, for the exact same reasons, either by the husband explicitly or by the society in respect of their differing positions in the family. Can this unequal treatment still be considered reasonable?
I really don't like arguing over words (2 Timothy 2:14), what really matters in my mind is reality, whatever you call it. And if the main reality of a concubine is a difference in inheritence, the question is not "is it ok to have a concubine", which is a meaningless question if "concubine" is undefined, but rather "is it ok to give two women different inheritence rights". That's a clearly defined question we can actually discuss without confusion.