FMIL is an abbreviation for "future mother-in-law." However, there are several synonyms you can use instead of FMIL that can spice things up in conversation. Some of the alternatives include prospect mother-in-law, pending mother-in-law, prospective mother-in-law, forthcoming mother-in-law, and anticipating mother-in-law. It all depends on your tone and the situation you are in. It's always good to have a range of synonyms because it adds variety to your conversations. So, the next time you are talking about your soon-to-be mother-in-law, consider using one of these synonyms instead of just the standard FMIL abbreviation.