Does "Sabbath" Mean "Week"?

In my post for last year's Pentecost, Pentecost 2008, I discussed the different Jewish reckonings of the Feast of Weeks. To quote my post:

"Here's the deal: Leviticus 23:11-16 tells the Israelites to present a wave sheaf offering to God on the day after the Sabbath. According to the passage, Pentecost occurs fifty days after that. The debate within first century Judaism was, 'Which Sabbath is Leviticus 23:11-16 talking about? Exactly when should we start counting to fifty?'"

The Pharisees interpreted the "Sabbath" to be the first Day of Unleavened Bread, so their Pentecost occurred fifty days after that and could fall on any day of the week. The Sadducees, however, treated the "Sabbath" as the weekly Sabbath (Saturday) during the Feast of Unleavened Bread, so their Pentecost always fell on a Sunday.

I've often assumed that there was no way to arbitrate this disagreement, but Ron Dart's program pointed something out that dramatically challenges the Pharisaic position. According to Leviticus 23:16, "You shall count until the day after the seventh sabbath, fifty days; then you shall present an offering of new grain to the LORD" (NRSV). In this passage, the fiftieth day (Pentecost) is the day after the seventh Sabbath. If that's the weekly Sabbath, then the day after it must be Sunday.

How do rabbinic Jews explain this? I don't know. Rashi (who refers to rabbinic traditions) doesn't explicitly deal with the issue, and I could not find a reference to Leviticus 23:16 in my Mishnah and Tosefta. My Jewish Study Bible and Jacob Milgrom's JPS commentary on Leviticus both agree that Pentecost was on a Sunday. Milgrom refers to Sifra 'Emor and Targum Onkelos, but I lack immediate access to those sources.

The impression I'm getting is that the rabbis interpreted "sabbath" in Leviticus 23:16 to mean a "week," not a weekly Sabbath. Milgrom states that. He also refers to the Septuagint, which translates Sabbath as "week" (Greek, hebdomados), thereby endorsing the position that the Pharisees later adopted. The Jewish Publication Society's Tanakh also translates Sabbath as "week," in accordance with the rabbinic practice that Orthodox, Conservative, and Reform Jews follow.

My problem is that the Hebrew already has a word for week, shavua. As a matter of fact, the Torah calls Pentecost the Feast of Weeks, or Shavuot (Exodus 34:22; Deuteronomy 16:10, 16). I cannot find a place where "Sabbath" means "week," but I could be wrong on this. Certainly the rabbis had some basis for their Pentecost reckoning, don't you think?