not worth a kers

from The Collaborative International Dictionary of English v.0.48

Kers \Kers\, Kerse \Kerse\, n.
   A cress. [Obs.] --Chaucer.
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   {Not worth a kers}. See under {Cress}.
      [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Cress \Cress\ (kr[e^]s), n.; pl. {Cresses} (kr[e^]s"[e^]z). [OE.
   ces, cresse, kers, kerse, AS. cresse, cerse; akin to D. kers,
   G. kresse, Dan. karse, Sw. krasse, and possibly also to OHG.
   chresan to creep.] (Bot.)
   A plant of various species, chiefly cruciferous. The leaves
   have a moderately pungent taste, and are used as a salad and
   antiscorbutic.
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   Note: The garden cress, called also {peppergrass}, is the
         {Lepidium sativum}; the water cress is the {Nasturtium
         officinale}. Various other plants are sometimes called
         cresses.
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               To strip the brook with mantling cresses spread.
                                                  --Goldsmith.
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   {Bitter cress}. See under {Bitter}.

   {Not worth a cress}, or {"not worth a kers."} a common old
      proverb, now turned into the meaningless "not worth a
      curse." --Skeat.
      [1913 Webster]