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

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

TAC
       Terminal Access Controller (ARPANET, MILNET)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

TAC
       Type Approval Code (IMEI, GSM, mobile-systems)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

TAC
       Technology Access Center (Rogue-Wave)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

TAC
       Technical Assistance Center (Cisco)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

TAC
       Terminal Access Circuit


The Free On-line Dictionary of Computing (30 December 2018):

TAC

   1. Translator Assembler-Compiler.  For Philco 2000.

   2. Terminal Access Controller.