predella
noun
pre·del·la pri-ˈde-lə 
: the base of an altarpiece
especially : one containing decorated panels depicting scenes related to the main panel or panels
Example Sentences
Recent Examples on the Web Saint Leopold and the predella appear to have been executed by another artist in the 1510s. 
Brigit Katz, Smithsonian Magazine, 13 Jan. 2020 The companion predella paintings, once attributed to Lorenzo di Credi, are now thought to be partly the work of Leonardo da Vinci. BostonGlobe.com, 9 Mar. 2018
Brigit Katz, Smithsonian Magazine, 13 Jan. 2020 The companion predella paintings, once attributed to Lorenzo di Credi, are now thought to be partly the work of Leonardo da Vinci. BostonGlobe.com, 9 Mar. 2018 Word History
Etymology
Italian, footrest, altar step, predella, from Langobardic (Germanic language of the Lombards) *predel-, *pretel-, lath, board; akin to Old High German bret board, bort plank, ship's side — more at board entry 1
First Known Use
1853, in the meaning defined above