priest: a person who officiates at a sanctuary for a god, standing between worshipers and that god by handling sacrifice, ruling on what is holy and clean, and teaching the god's instruction
A priest works at the meeting point between people and a god. The core task is at the altar and sanctuary: he handles the offerings, manages the blood and the holy things, and declares who and what is clean or unclean so that worship can go forward. In Israel the office settles on Aaron's line, with the wider tribe of Levi serving alongside, and the priest is also a judge of hard cases and the keeper and teacher of God's instruction.
This one idea, an officiant who mediates at a cult site, holds across every use of the word, so it is one meaning carried over a wide range of people. The same term names the ordinary altar priest, the senior priest who heads the whole order, the priest of a foreign god, the priest who staffs an outlawed Israelite shrine, and even a high royal official at the king's side. Hebrew keeps a separate, openly hostile word for an idol's priest, yet it does not reach for it here. The plain word itself passes no verdict; the verse's setting, or the name of the god attached to it, tells you whether the priest is approved or condemned.
The word also stretches to a whole people and to a coming king. Israel is called a kingdom of priests, set apart to carry God's presence to the nations, and a royal figure is named a priest forever in the line of Melchizedek. These are real extensions of the single office, not separate meanings of the word.
Nuances
Whether the word in the Davidic court verses (2 Samuel 8:18; 20:26; 1 Kings 4:5) means these men literally held priestly office, or carries an older, broader sense of a high royal official close to the king. The parallel in 1 Chronicles 18:17 replaces it with a phrase meaning the chief officials at the king's hand, which many take as the Chronicler's own clarification that a civil court role is in view; others hold that in early Israel the king and his sons did exercise a genuine, if irregular, priestly function before the office was fully restricted to Aaron's line.
- contestedThe word here denotes a high royal official or minister of state, not a sacrificing priest, carrying an older Semitic sense of a royal administrator, as the Chronicler's paraphrase indicates.; Roland de Vaux, Ancient Israel (1961), 113-114, 353-355
- contestedThe word keeps its ordinary priestly sense: in the early monarchy the king and his sons did discharge real, if exceptional, cultic functions, and later orthodoxy found this scandalous.; Julius Wellhausen, Prolegomena to the History of Israel (ET 1885), 121-124; Gordon J. Wenham, "Were David's Sons Priests?" ZAW 87 (1975): 79-82
- contestedThe Hebrew preserves an authentic older usage that both the Chronicler and the Old Greek translator found necessary to paraphrase away, which is itself evidence that the early sense was broader than the later Aaronide ideology allowed.; P. Kyle McCarter Jr., II Samuel, AB 9 (1984), 255