undergird

From under- +‎ gird.

undergird (third-person singular simple present undergirds, present participle undergirding, simple past and past participle undergirded)

1. To strengthen, secure, or reinforce by passing a rope, cable, or chain around the underside of an object.
2. To give fundamental support; provide with a sound or secure basis; provide supportive evidence for.
3. To lend moral support to.
4. To secure below or underneath.

• shore up
• fortify
• succour

• undermine