From multi- +‎ marginal.

multimarginal (not comparable)

1. marginal in multiple ways
   • 2015, Maria Colombo, Federico Stra, “Counterexamples in multimarginal optimal transport with Coulomb cost and spherically symmetric data”, in arXiv‎^[1]:

     We disprove a conjecture in Density Functional Theory, relative to multimarginal optimal transport maps with Coulomb cost.