(A), means simply a piece of rag or skin. (Latin, pannus; Greek, penos.) In law it means a piece of parchment containing the names of jurors. To empanel a jury is to enter their names on the panel or roll. The panels of a room are the framed wainscot which supplies the place of tapestry, and the panels of doors are the thin boards like wainscot.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894