Verses with the word priesthood in the Old Testament (8 verses):

Exodus 40:15
And thou shalt anoint them, as thou didst anoint their father, that they may minister unto me in the priest's office: for their anointing shall surely be an everlasting priesthood throughout their generations.

Numbers 16:10
And he hath brought thee near to him, and all thy brethren the sons of Levi with thee: and seek ye the priesthood also?

Numbers 18:1
And the LORD said unto Aaron, Thou and thy sons and thy father's house with thee shall bear the iniquity of the sanctuary: and thou and thy sons with thee shall bear the iniquity of your priesthood.

Numbers 25:13
And he shall have it, and his seed after him, even the covenant of an everlasting priesthood; because he was zealous for his God, and made an atonement for the children of Israel.

Joshua 18:7
But the Levites have no part among you; for the priesthood of the LORD is their inheritance: and Gad, and Reuben, and half the tribe of Manasseh, have received their inheritance beyond Jordan on the east, which Moses the servant of the LORD gave them.

Ezra 2:62
These sought their register among those that were reckoned by genealogy, but they were not found: therefore were they, as polluted, put from the priesthood.

Nehemiah 7:64
These sought their register among those that were reckoned by genealogy, but it was not found: therefore were they, as polluted, put from the priesthood.

Nehemiah 13:29
Remember them, O my God, because they have defiled the priesthood, and the covenant of the priesthood, and of the Levites.