IPA: //ˈsuːpərˌstrætəm//
KK: /ˈsuːpərˌstrætəm/
A layer that is placed on top of another layer, often used in linguistics to describe a language that influences another language.
The superstratum of the local language was influenced by the invaders' dialect.
Superstratum → It is formed from "super-" (meaning above or over) and "stratum" (from Latin, meaning layer). The word refers to a layer that is situated above another layer.
Think of something that is 'above' ('super-') another 'layer' ('stratum') — that's why superstratum means an upper layer.