[1] : WordNet (r) 2.0

beef up
     v : make strong or stronger; "this exercise will strengthen your
         upper body"; "strenghten the relations between the two
         countries" syn: strengthen, fortify ant: weaken
see also:
strengthen fortify weaken 

[2] : Moby Thesaurus II by Grady Ward, 1.0

59 moby thesaurus words for "beef up":
   accelerate, aggrandize, aggravate, augment, blow up, boost, brace,
   brace up, buttress, case harden, complicate, concentrate, condense,
   confirm, consolidate, deepen, double, enhance, enlarge, exacerbate,
   exaggerate, expand, extend, fortify, gird, harden, heat up,
   heighten, hop up, hot up, intensify, invigorate, jazz up, key up,
   magnify, make complex, multiply, nerve, prop, ramify, redouble,
   refresh, reinforce, reinvigorate, restrengthen, sharpen, shore up,
   soup up, steel, step up, stiffen, strengthen, support, sustain,
   temper, toughen, triple, undergird, whet

Ball Up >> B Words
Ball Up, definition of term: Ball Up
ball+up_pag1.html

Bang Up >> B Words
Bang Up, definition of term: Bang Up
bang+up_pag1.html

Backed Up >> B Words
Backed Up, definition of term: Backed Up
backed+up_pag1.html

Back Up >> B Words
Back Up, definition of term: Back Up
back+up_pag1.html

Ante Up >> A Words
Ante Up, definition of term: Ante Up
ante+up_pag1.html

Act Up >> A Words
Act Up, definition of term: Act Up
act+up_pag1.html