late 13c., "flaming, full of fire," from Middle English fier "fire" (see fire (n.)) + -y (2). The spelling is a relic of one of the attempts to render Old English "y" in fyr in a changing system of vowel sounds. Other Middle English spellings include firi, furi, fuiri, vuiri, feri. From c. 1400 as "blazing red." Of persons, from late 14c. Related: Fieriness. As adjectives Old English had fyrbære "fiery, fire-bearing;" fyren "of fire, fiery, on fire;" fyrenful; fyrhat "hot as fire."
"pile or heap of wood or other combustible materials for burning a dead body," 1650s, from Latin pyra and directly from Greek pyra (Ionic pyrē) "funeral pyre; altar for sacrifice; watch-fire; hearth; any place where fire is kindled," from pyr "fire" (from PIE root *paewr- "fire," source also of fire (n.)). Related: Pyral.