Usage: "I would not like to eat that pie as it looks all festy since you dropped it on the ground."
Is the colloquial Australian term 'festy' actually a word?
Also, is it used elsewhere in the world?
The Merriam Webster hasn't heard of it, but the Urban Dictionary lists it with the first two senses as back-constructions of "fester", respectively:
As English seems to expand much more than it contracts, it seems that in another decade or so if not less, Webster will list it and then Oxford.