underpinning

1 an immaterial thing upon which something else rests the underpinnings of the theory have recently been called into question Synonyms basis, bedrock, bottom, cornerstone, footing, foundation, ground, groundwork, keystone, root, base, warp, warp and woofRelated Words anchorage, bed, brace, bulwark, buttress, framework, infrastructure, mount, prop, shore, stay, substratum, substructure, support; assumption, justification, premise (also premiss), presumption, presupposition, rationale, supposition, theory, thesis, warrant; backbone, center, core, cornerstone, eye, focus, heart, hub, kernel, keystone, nucleus, seat; essence, quintessence, soul, touchstone

2 a structure that holds up or serves as a foundation for something else the underpinnings of the bridge were seriously damaged in the collision Synonyms brace, buttress, mount, mounting, prop, reinforcement, shore, spur, stay, supportRelated Words shoring; column, pedestal, pilaster, pillar; arch, bolster, bracket, cantilever, girder; bearing; crutch, peg, post, stake, stanchion, stand, stilt, strut, truss; base, foundation, frame