A Sabbath-day is a day kept holy as the Sabbath.

That is the correct spelling of "sabbath" or Sabbath, a weekly religious day.

the sabbath is a holy day of rest

The Torah establishes the Sabbath with commandments to keep the Sabbath day, to remember the Sabbath day, and constraining what may be done on the Sabbath. And, in the Jewish liturgy that emerged from this framework, the Sabbath morning service includes a Torah reading where, traditionally, about 1/52 of the Torah is read, so that over the course of the year, every Jew who attends Sabbath services on a regular basis will hear (and, we hope, learn from) the entire Torah.

The phrase "sabbath day"comes from the Bible. Sabbath means "to rest" and the sabbath day was instituted by God during creation week when He created the seventh day and made it a holy day for rest.

God also included the sabbath day into the ten commandments.