an obsolete metric prefix denoting ten million (107). It was coined from the Greek hebdomos, seventh. A group of seven is sometimes called a hebdomad, a word related to the French hebdomadaire, weekly.
Found on http://www.unc.edu/~rowlett/units/dictH.html


Hebdo- is an archaic metric prefix equal to 107. It is derived from the Greek hebdοmos (ἕβδομος) meaning seventh. The original definition of the meter established one Hebdometer as the distance from the north pole to the equator. ...
Found on http://en.wikipedia.org/wiki/Hebdo-
No exact match found