Undergird vs. Underpin — What's the Difference?

Secure or fasten from the underside, especially by a rope or chain passed underneath.

Support (a building or other structure) from below by laying a solid foundation below ground level or by substituting stronger for weaker materials.

To support or strengthen from beneath.

Support, justify, or form the basis for

To strengthen, secure, or reinforce by passing a rope, cable, or chain around the underside of an object.

To support from below, as with props, girders, or masonry.

(figurative) To give fundamental support; provide with a sound or secure basis; provide supportive evidence for.

To give support or substance to

To lend moral support to.

(transitive) To support from below with props or masonry.

To secure below or underneath.

To give support to; to corroborate.

To bind below; to gird round the bottom.

To lay stones, masonry, etc., under, as the sills of a building, on which it is to rest.

Lend moral support to

To support by some solid foundation; to place something underneath for support.

Make secure underneath;

Support from beneath

Support with evidence or authority or make more certain or confirm;