underpin

Concise Oxford English Dictionary © 2008 Oxford University Press:
underpin/ʌndəˈpɪn/

▶verb (underpins, underpinning, underpinned)

• 1 support (a structure) from below by laying a solid foundation or substituting stronger for weaker materials.

• 2 support, justify, or form the basis for.

– derivatives
underpinning noun.