Wu is a picture of a signal staff with three streamers; hence the idea of a warning not to do something.

Shih is composed of two obsolete characters meaning to bring together the fragrance of grain.

80H.	免	罪	處	${\displaystyle \scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right\}\,}}$	and so avoid being punished.
	Mien3	tsui4	ch'u3
	Avoid	guilt	punishment

Mien is not given in the Shuo Wên, and is supposed to be a contraction of an obsolete word with the same meaning.

Tsui was originally composed of 辛 hsin acrid and 自 tzŭ self. It has been suggested that the change was brought about by taboo, as in many other characters.

Ch'u see line 10.