Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : Free On-Line Dictionary of Computing

TAC
     
        1. Translator Assembler-Compiler.  For {Philco 2000}.
     
        2. {Terminal Access Controller}.