superstratum

from WordNet (r) 3.0 (2006)

superstratum
    n 1: any stratum or layer superimposed on another [syn:
         {superstrate}, {superstratum}]
    2: the language of a later invading people that is imposed on an
       indigenous population and contributes features to their
       language [syn: {superstrate}, {superstratum}]

from The Collaborative International Dictionary of English v.0.48

Superstratum \Su`per*stra"tum\, n.; pl. {Superstrata}. [NL.: cf.
   L. supersternere, superstratum, to spread upon. See {Super-},
   and {Stratum}.]
   A stratum, or layer, above another.
   [1913 Webster]

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