weakly, feeble, fragile, infirm, delicate, decrepit, fallible, imperfect, breakable, sapless, more...

robust, sturdy, strong, hardy

weak, fragile, delicate, frangible, flimsy, breakable, brittle, crumbly, more...

shaky infirm,   weak or feeble,   physically weak,   weak to,   weak with old age,   thin and weak,   weak looking,   being weak,   looking weak,   weak or unsteady,   weak constitution