Source : Webster's Revised Unabridged Dictionary (1913)

Rest-harrow \Rest"-har`row\ (-h?r`r?), n. (Bot.)
   A European leguminous plant ({Ononis arvensis}) with long,
   tough roots.

Source : WordNet®

rest-harrow
     n 1: Eurasian plant having loose racemes of pink or purple
          flowers and spiny stems and tough roots [syn: {restharrow},
           {Ononis spinosa}]
     2: European woody plant having pink flowers and unifoliate
        leaves and long tough roots; spreads by underground
        runners [syn: {restharrow}, {Ononis repens}]