upper, higher, or highest: set physically above something else, or raised above others in rank
At its plainest this word simply marks the higher of two things. A building has an upper room and a lower one; a city sits on the higher ridge while its twin sits below; water runs from an upper pool to a lower channel. The word picks out whichever member of a pair is on top.
From that physical sense it stretches naturally to rank. To be highest is to be raised above everyone around you. Israel is promised it will stand high above all the nations, the king is set higher than all other kings, and the temple is the most prominent thing on the skyline. In each case the picture of physical height carries the meaning of status: the thing on top is the one that matters most.
These ordinary uses share one idea, being above. That same idea, pushed to its limit, becomes the great title for God explored under the next meaning.