“What’d anyone want to do that for?” said Nanny.“Practice” said Granny.“Practice? What for?” said Magrat.“I expect we’ll find out presently.” said Granny gnomically.
Expressed in or of the nature of short, pithy maxims or aphorisms:
I think the second definition is more appropriate to Pratchett’s use.
Now for my favorite part, etymology:
from Greek root of gignoskein “to come to know” and gnostos “knowable.” Which gives us “gnostic” for one who believes in God, and “agnostic” for one who thinks it’s impossible to know for sure.
Once again, thanks to etymonline.