Yours, Etc.: Origins and Uses of 8 Sign-Offs
painting on a wall, 1921, short for mural painting (1850), from mural (adj.) "pertaining to walls" (mid-15c.), from Latin muralis "of a wall," from murus "wall" (Old Latin moiros, moerus), from PIE *mei- "to fix; to build fences or fortifications" (cf. Old English mære "boundary, border, landmark;" Old Norse -mæri "boundary, border-land;" Latin munire "to fortify, protect").
mural mu·ral (myur'əl)
Of or relating to the wall of any cavity.
A painting, usually large, made directly on a wall.
Note: The Mexican artist Diego Rivera was noted for his production of murals.