[tay]

Hi
I had a question I was wondering if someone could answer for me.

There's a word for this but I don't know what it is. It's when you put letters together and, when pronounced, have the same results as an actual word. For example:
xtc = ecstasy
xs = excess

Some call this acrostics but I don't think that's correct. Acrostics is when you have letters at the beginning of a group of words or sentences that spell out something that pertains to those words or sentences. Like this:
North
East
West
South ("NEWS")

So, does anyone know what that word is?
(note, this is not a riddle, I genuinely would like to know!)

Thanks!