Source : Webster's Revised Unabridged Dictionary (1913)

Clevis \Clev"is\, n. [Cf. {Cleave} to adhere, {Clavel}.]
   A piece of metal bent in the form of an oxbow, with the two
   ends perforated to receive a pin, used on the end of the
   tongue of a plow, wagen, etc., to attach it to a draft chain,
   whiffletree, etc.; -- called also {clavel}, {clevy}.

Source : WordNet®

clevis
     n : a coupler shaped like the letter U with holes through each
         end so a bolt or pin can pass through the holes to
         complete the coupling; used to attach a drawbar to a plow
         or wagon or trailer etc.