v.，为…根居，基础；v.立于…最下面
Merriam-Webster Online Dictionary
underlie (verb)transitive verb
1.
archaic to be subject or amenable to
2.
to lie or be situated - under
3.
to be at the basis of form the foundation of - support ideas underlying the revolution
4.
to exist as a claim or security superior and prior to (another)