Source : Webster's Revised Unabridged Dictionary (1913)

Couth \Couth\ (k??th), imp. & p. p. of {Can}. [See {Can}, and
   cf. {Uncouth}.]
   Could; was able; knew or known; understood. [Obs.]

         Above all other one Daniel He loveth, for he couth well
         Divine, that none other couth; To him were all thing
         couth, As he had it of God's grace.      --Gower.

Source : WordNet®

couth
     adj : used facetiously