The term adstratum refers to a language which is equal in prestige to another. Generally the term is used only when speaking about languages in a particular country or geopolitical region. For example, early in England's history, English and Norse had an adstratal relationship.

The phenomenon is relatively rare today, since modern nations generally have only one dominant language (often derived from the dialect of the capital). In India, where dozens of languages are widespread, many could be said to share an adstratal relationship, although Hindi is certainly dominant. A more accurate example would be the situation in Belgium, where the French and Dutch languages have roughly the same status, and could justifiably be called adstrates.

See Substratum and Superstratum.