extension field

noun1

1. •
   A field L which contains a subfield K, called the base field, from which it is generated by adjoining extra elements.

   • Suppose F is a subfield of the field K. Then K is called an extension field of F. So, for instance, GF(4) and GF(8) are extension fields of GF(2), although GF(8) is not an extension field of GF(4). — 1992