The word Tclet is pronounced to rhyme with chicklet, a little chicken, or a wad of the famous chewing gum. There is no intended connection with chewing gum here, although Tclets also are GUI. You say it so: tick-let. The word is always written with a capital T.
The word Tcl, the name of the language these little programs are written in, is pronounced either tee-see-el or tick'el. It's an abbreviation for Tool Command Language. We will know what you're talking about if you use either of these pronounciations.