c.1200, from O.E. conj.
oþþe "either, or," related to O.N.
eða, O.H.G.
odar, Ger.
oder, Goth.
aiþþau "or." This was extended in early M.E. with an
-r ending, perhaps by analogy of other "choice between alternative" words that ended this way (
either, whether), then reduced to
oþþr, at first in unstressed situations (commonly thus in Northern and Midlands Eng. by 1300), and finally reduced to
or, though
other survived in this sense until 16c. The contraction took place in the second term of an alternative, such as
either ... or, a common construction in O.E., where both words originally were
oþþe (see
nor).
[awr] 
Heraldry.