IPA: //sʌbˈsɜːrfɪs//
KK: /sʌbˈsɜrfɪs/
Relating to or located beneath a surface, especially under the ground or water.
The subsurface layers of soil are important for plant growth.
Material that is located just below the surface of the ground, such as soil or rock that is not visible from above.
The construction project required drilling into the subsurface to assess the soil conditions.
Subsurface → It is formed from "sub-" (meaning under) and "surface" (from Latin "superficies", meaning the outer face or appearance). The word "subsurface" refers to the layer that is located beneath the surface.
Think of something that is located 'under' ('sub-') the 'outer layer' ('surface') — that's what subsurface means.