DuckCorp Dico

Found one definition

1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   Tac \Tac\, n. [Cf. Tack, n., 4.] (O. Eng. Law)
      A kind of customary payment by a tenant; -- a word used in
      old records. --Cowell. --Burrill.
      [1913 Webster] Tacamahac