Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "might and main":
   amperage, armipotence, authority, beef, black power, brute force,
   charge, charisma, clout, cogence, cogency, compulsion, dint, drive,
   duress, effect, effectiveness, effectuality, effort, elbow grease,
   endeavor, energetically, energy, exertion, flower power, force,
   force majeure, forcefully, forcefulness, forcibly, full blast,
   full force, hard pull, hardly, influence, long pull, main force,
   main strength, mana, might, mightily, mightiness, moxie, muscle,
   muscle power, nerve and sinew, pains, pizzazz, poop, potence,
   potency, potentiality, power, power pack, power structure,
   power struggle, powerfully, powerfulness, prepotency,
   productiveness, productivity, puissance, pull, punch, push, sinew,
   steam, strength, strong arm, strongly, superiority, superpower,
   trouble, validity, vehemence, vigor, vigorously, vim, virility,
   virtue, virulence, vitality, wattage, weight