The Collaborative International Dictionary of English v.0.48:

Pat \Pat\, v. t. [imp. & p. p. Patted; p. pr. & vb. n.
   Patting.] [Cf. G. patschen, Prov. G. patzen, to strike,
   tap.]
   To strike gently with the fingers or hand; to stroke lightly;
   to tap; as, to pat a dog.
   [1913 Webster]

         Gay pats my shoulder, and you vanish quite. --Pope.
   [1913 Webster]