Where does “φέρετρον” come from?

φέρετρον (Koine Greek) comes from Ancient Greek φέρετρον, from Ancient Greek φέρω, from Proto-Hellenic pʰérō, from Proto-Indo-European bʰéreti, from Proto-Indo-European bʰēr- — shiny, light brown.

φέρετρον (Koine Greek): bier; litter; frame