literally "of Pieria," 1590s, from Latin Pierius "Pieria," from Greek Pieria, district in northern Thessaly, reputed home of the Muses (who also were known as Pierides); thus "pertaining to poetry."
A little Learning is a dang'rous Thing;
Drink deep, or taste not the Pierian Spring:
[Pope, "Essay on Criticism," 1711]
The name is ultimately from PIE *peie- "be fat, swell" (see fat (adj.)).