1) Back up 2) Lend moral support to 3) Make secure underneath 4) Support 5) To give fundamental support 6) To lend moral support to 7) To secure below or underneath 8) To strengthen 
• (v. t.) To blind below; to gird round the bottom.
[v] - lend moral support to 2. [v] - make secure underneath
to strengthen; secure, as by passing a rope or chain under and around: to undergird a top-heavy load. · to give fundamental support; provide with a sound or secure basis: ethics undergirded by faith.