No definitive etymology can be suggested. An eventual connection with biri “between” is not to be excluded (“to see” < “to distinguish”), but has no external etymological support as the Akkadian preposition lacks Semitic etymology.
On reconstruction see Kogan 2015:219.
No reliable Semitic etymology can be suggested. May be related to Arb. bry 'to fatigue, to jade one’s she-camel, to make it lose flesh; to render lean, emaciated'.