Frequently Asked Question List for TeX
Lamport never recommended how one should pronounce LaTeX, but a lot of people pronounce it “Lay TeX” or perhaps “Lah TeX” (with TeX pronounced as the program itself; see the rules for TeX). It is definitely not to be pronounced in the same way as the rubber-tree gum (which would be “lay teks”).
The LaTeX2e logo is supposed to end with an ε; nevertheless, most people pronounce the name as “LaTeX-two-ee”.
FAQ ID: Q-latexpronounce