Bi-cycle = 2 wheels
Bi-sexual = 2 distinct sexual preferences
Bi-centenial = 2 hundred years
Bi-lateral = 2 sides
Bi-sect = divide into 2 parts
Bi-weekly = every 2 weeks
From most examples I can find, Bi is distinctly relative to a the specific quantity of 2, and doesn't seem to be used in similar circumstance to the word "twice", which would seem to be more appropriate in this case.
In other words, "Twice weekly" is far more descriptive as it implies a multiple, ie. "twice as much", "twice in one day", etc., whereas the specific quantity of 2, as applied to "2 weekly" says just what sounds like. One time every 2 weeks.
RandyT
(I just made all that up, but it sounds good, doesn't it?

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