The frame that holds many in order — storage standing upright, everything visible.
Middle Dutch rec (a framework, a rack), related to the verb rekken (to stretch, to reach); a rack is named for the stretching-out of its frame, everything on it held in reach and in view.
The frame that holds many things in order, storage standing upright with everything visible. The stretching in the root is literal: a rack is a shape pulled taut so nothing on it is hidden behind anything else.