subrogation(n = noun.act) - (law) the act of substituting of one creditor for another;
is a kind of commutation, exchange, substitution
Derived form verb subrogate₁

   The act of subrogating. Bouvier. Burrill. Abbott. [1913 Webster]

subrogation, n. Law the substitution of one party for another as creditor, with the transfer of rights and duties.

Derivative:
subrogate v.tr.

Etymology:
LL subrogatio f. subrogare choose as substitute (as SUB-, rogare ask)