Old English bær (West Saxon), ber (Anglian) "handbarrow, litter, bed," from West Germanic *bero (source also of Old Saxon, Old High German bara, Old Frisian bere, Middle Dutch bare, Dutch baar, German Bahre "bier"), from PIE root *bher- (1) "to carry."
The original sense is "wooden frame on which to carry a load," and it is related to bear (v.). Specific sense of "framework on which a coffin or corpse is laid before burial" was in late Old English and predominated from c. 1600. The spelling altered from c. 1600 under influence of French bière, from Old French biere, from Frankish *bera, from the same Germanic source.