Boyd’s Bible Dictionary:

(running). Priests divided into twenty-four classes, courses, or orders (1 Chron. 24). [ASIA.]

Concise Bible Dictionary:

David divided the priests into 24 courses: 16 of them were of the house of Eleazar, and 8 of Ithamar. A list of them, under the name of each head, is given in 1 Chronicles 24:6-196And Shemaiah the son of Nethaneel the scribe, one of the Levites, wrote them before the king, and the princes, and Zadok the priest, and Ahimelech the son of Abiathar, and before the chief of the fathers of the priests and Levites: one principal household being taken for Eleazar, and one taken for Ithamar. 7Now the first lot came forth to Jehoiarib, the second to Jedaiah, 8The third to Harim, the fourth to Seorim, 9The fifth to Malchijah, the sixth to Mijamin, 10The seventh to Hakkoz, the eighth to Abijah, 11The ninth to Jeshua, the tenth to Shecaniah, 12The eleventh to Eliashib, the twelfth to Jakim, 13The thirteenth to Huppah, the fourteenth to Jeshebeab, 14The fifteenth to Bilgah, the sixteenth to Immer, 15The seventeenth to Hezir, the eighteenth to Aphses, 16The nineteenth to Pethahiah, the twentieth to Jehezekel, 17The one and twentieth to Jachin, the two and twentieth to Gamul, 18The three and twentieth to Delaiah, the four and twentieth to Maaziah. 19These were the orderings of them in their service to come into the house of the Lord, according to their manner, under Aaron their father, as the Lord God of Israel had commanded him. (1 Chronicles 24:6‑19). The Levites were divided in a similar manner (1 Chron. 23). David also instituted in the army a kind of militia, each course to serve a month (1 Chron. 27).
Twenty-four is a number seldom found in the scripture: there may therefore, as to number, be an allusion to the 24 courses of priests in the 24 elders seated on thrones in Revelation 4:44And round about the throne were four and twenty seats: and upon the seats I saw four and twenty elders sitting, clothed in white raiment; and they had on their heads crowns of gold. (Revelation 4:4), representing the complete heavenly priesthood.

Strong’s Dictionary of Greek Words:

from 2184; diurnality, i.e. (specially) the quotidian rotation or class of the Jewish priests' service at the Temple, as distributed by families
KJV Usage: