un‧der‧pin past tense and past participle underpinned, present participle underpinning [transitive]
to give strength or support to something and to help it succeed:
the theories that underpin his teaching method
America's wealth is underpinned by a global system which exploits the world's poor.
to put a solid piece of metal under a wall or house in order to make it stronger
—underpinning noun [uncountable and countable]