"Bad" words

It’s been a pet peeve of mine for a long time. But, to my chagrin, I just heard it in a Domino’s Pizza commercial (and since it was on TV, I figured it counts as entertainment!)
The word “ginormous.”
It’s not a word.
I’m not even sure if I spelled it correctly since I can’t look it up in the dictionary. Do you use it? I have friends who do, and I secretly sit there and think, “What’s wrong with gigantic or enormous?… they’re good words, too.”
I was the same way with “guesstimate.” Seemed like a stupid, made-up word which completely laughed in the face of the perfectly adequate words, “guess” and “estimate.” Do they not deserve their due?
Imagine my surprise when I flipped open my Miriam Webster’s Collegiate Dictionary 10th Edtition, and there it is. Guesstimate: An estimate made without adequate information. AND… it’s been in there since 1923 – older than I am.
I suppose I’ll have to accept that one now – my apologies to “guesstimate.”
But “ginormous”? What is it? Where does it fall in the “big” hierarchy? Is it “big,” “huge,” “massive,” “gigantic,” “enormous,” “ginormous”?
If that’s the case, it begs the question: Do we really need a “ginormous” pizza?