The English Oxford Dictionaries’ definition of the word 'until' lists the following as its etymology:
Middle English: from Old Norse und 'as far as' + till (the sense thus duplicated)
Etymonline similarly states:
c.1200, from O.N. und "as far as, up to" (related to O.E. end; see end) + till "until, up to".
Looking at the two entries, it seems that until is made up of two roots which mean the same thing, rendering the word something of a tautology ('up to up to'). Or does it? Etymonline also states that it is related to the word end which would effectively make the etymology of until mean, 'up to the end'. This makes some sort of sense.
The OED (online), however, does not list until as being related to end. Moreover, Etymonline does not mention und in its entry for end either, which makes things a little confusing.
So, is until something of a tautology? If so, is it unique in this aspect?