Originally: a layer or structure that lies below the base, floor, or lowest point of something else. Later chiefly: specifically the rock strata beneath the sea bed.
adjectiveˌsʌbˈbɒtəm
Below the lowest level or bottom of something, (now especially) below the sea bed.
Origin
Late 19th century. From sub- + bottom.
Definition of sub-bottom in US English:
sub-bottom
nounˌsʌbˈbɒtəm
Originally: a layer or structure that lies below the base, floor, or lowest point of something else. Later chiefly: specifically the rock strata beneath the sea bed.
adjectiveˌsʌbˈbɒtəm
Below the lowest level or bottom of something, (now especially) below the sea bed.