unsound, a. defective, impaired; [sophistical], [fallacious], [illogical], untenable.
unsparing, a. [liberal], ungrudging, profuse; [severe], [unmerciful].
unspeakable, a. ineffable, [unutterable], [inexpressible].
unspotted, a. [spotless], [pure].
unstable, a. [insecure], [unsteady], [irresolute], [inconstant], [erratic].
unsteadfast, a. [unstable], [inconstant], [wavering], [irresolute].
unsteady, a. [inconstant], [precarious], [wavering], [variable], [vacillating], wabbly.
unstinted, a. [plentiful].
unstudied, a. extemporaneous, extempore, [impromptu], [offhand].
unsubmissive, a. insubordinate, [refractory].