From שבת (“Sabbath, Shabbat, Saturday”). The Hebrew name is such because the planet is named after the Roman god Saturn in most European languages. The sixth day of the week (seventh in Jewish tradition), Saturday, was also dedicated to the god Saturn (see dies Saturni), before being renamed "Sabbath" (dies Sabbati), as in Hebrew, after the Christianization of the Roman Empire. Today, European languages are split in their name for the day, with the majority using a derivative of שבת, and a minority, including English, retaining the dedication to Saturn. The name "שבתאי" is therefore a calque of sorts of the name "Saturn," reinterpreting the planet's name as being taken from the word Saturday instead of the Roman god.
שַׁבְּתַאי • (shabtá'i) m