Definition of "undergird"

undergird

verb
third-person singular simple present undergirds, present participle undergirding, simple past and past participle undergirded or undergirt
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.
  Quotations
  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.