Substratum/ˈsʌbstreɪtəm/ Definition 1 of 3Pro Tip 1/3Physical layer Refers to real, tangible layers, like rock or sediment, not abstract ones. Archaeologists studied the substratum to understand the site's history. Pro Tip 2/3Technical contexts Mostly used in specialized fields such as geology or construction. The engineer analyzed the substratum for the new highway. Pro Tip 3/3Supportive nature Emphasizes the supporting role of a layer beneath another. The greenhouse was constructed on a strong substratum.