"What is the average?"
Translation:Cad é an meán?
Well, given that "Meán Fómhair" is mid-autumn, that's the median, not the mean, in the mathematical sense. And what is "normal" would be the modal average, no?
FWIW, English "mean" (in this sense) comes from Old French "meien" which comes from Latin "medianus", and itself had stronger connotations of what we now call the median, not the mean.
I daresay the Irish got "meán" from the same source, somewhere along the way.