N impotence, inability, disability, disablement, impuissance, imbecility, incapacity, incapability, inaptitude, ineptitude, incompetence, unproductivity, indocility, invalidity, disqualification, inefficiency, wastefulness, telum imbelle, brutum fulmen, blank, blank cartridge, flash in the pan, vox et proeterea nihil, dead letter, bit of waste paper, dummy, paper tiger, Quaker gun, inefficacy, failure, helplessness, prostration, paralysis, palsy, apoplexy, syncope, sideration, deliquium, collapse, exhaustion, softening of the brain, inanition, emasculation, orchiotomy, orchotomy, cripple, old woman, muff, powder puff, creampuff, pussycat, wimp, mollycoddle, eunuch, powerless, impotent, unable, incapable, incompetent, inefficient, ineffective, inept, unfit, unfitted, unqualified, disqualified, unendowed, inapt, unapt, crippled, disabled, armless, harmless, unarmed, weaponless, defenseless, sine ictu, unfortified, indefensible, vincible, pregnable, untenable, paralytic, paralyzed, palsied, imbecile, nerveless, sinewless, marrowless, pithless, lustless, emasculate, disjointed, out of joint, out of gear, unnerved, unhinged, water-logged, on one's beam ends, rudderless, laid on one's back, done up, dead beat, exhausted, shattered, demoralized, graveled, helpless, unfriended, fatherless, without a leg to stand on, hors de combat, laid on the shelf, null and void, nugatory, inoperative, good for nothing, ineffectual, inadequate, inefficacious, der kranke Mann, desirous still but impotent to rise, the spirit is willing but the flesh is weak.

For further exploring for "helplessness" in Webster Dictionary Online