The Hebrew verb atsal (H680) means to set apart, reserve, withhold, or take from a larger portion. It is used of setting aside a portion of the Spirit for the elders of Israel (Numbers 11:17), and of reserving or keeping back something from a larger whole.
The most theologically rich use of atsal is in Numbers 11:17, where God promises to take of the Spirit that rested on Moses and put it on the seventy elders. This is not a diminishment of Moses's spirit but a sharing — a principle that foreshadows Pentecost, where the Spirit poured out on all flesh. The God who sets apart also distributes — sovereignly apportioning His gifts to build up His people.