Those which have the value of independent words, inasmuch as
   the simple words are either not used at all, or are rarely, or at least
   much less frequently, used; as, unavoidable, unconscionable,
   undeniable, unspeakable, unprecedented, unruly, and the like; or
   inasmuch as they are used in a different sense from the usual meaning
   of the primitive, or especially in one of the significations of the
   latter; as, unaccountable, unalloyed, unbelieving, unpretending,
   unreserved, and the like; or inasmuch as they are so frequently and
   familiarly used that they are hardly felt to be of negative origin; as,
   uncertain, uneven, and the like.