to wait on someone in trusted, honored service: to attend a person of rank or to minister before God
This is the dignified word for service. It pictures the trusted attendant who stays close to a superior and carries out his wishes: the steward who runs a great household, the young man who follows a master and learns from him, the courtier who waits in a king's presence. The service is honorable, not menial, and it usually puts the servant in a position of standing and confidence.
Its two settings are the same kind of service aimed in two directions. One is service to a person of rank, where the word names attendants like Joseph in Potiphar's house, Joshua at Moses' side, or the officials around a king. The other is service to God, where it becomes the standard term for the priests and Levites who do the work of worship at the sanctuary. The connection is direct: ministering before the LORD is pictured as personal attendance on the King of kings, done by those granted the privilege of drawing near.
Because the same word covers both, Scripture can move easily between a servant attending a person and a priest attending God, and the reader is meant to feel the dignity in both. This is what sets it apart from the ordinary word for serving as a slave or laborer.