WordNet (r) 3.0 (2006):

Tl
    n 1: a soft grey malleable metallic element that resembles tin
         but discolors on exposure to air; it is highly toxic and is
         used in rodent and insect poisons; occurs in zinc blende
         and some iron ores [syn: thallium, Tl, atomic number
         81]

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

TL
       Telecommunication Leadership [standard] (QuEST)


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

TL
       Transform and Lighting (3D), "T&L"

       TL;DR        Too Long; Didn't Read (slang, Usenet, IRC)