undergird

Etymology

From under- + gird.

verb

1. To strengthen, secure, or reinforce by passing a rope, cable, or chain around the underside of an object.
2. (figurative) To give fundamental support; provide with a sound or secure basis; provide supportive evidence for.
   For fiction, documentary, verse, and essay, she undergirds entertaining images and stories with profound themes of ecological responsibility and challenge to the suppression of human rights. 2015, Mary Ellen Snodgrass, Barbara Kingsolver: A Literary Companion, McFarland, page 3
3. To lend moral support to.
4. To secure below or underneath.