Do not slander an honest person with baseless words.
Tips
history
衊 is not used independently in modern Chinese; its 'to smear / slander' sense survives in 污衊, today usually written with the simpler 污蔑. It combines the blood radical 血 with 蔑, which also supplies the sound.
register
Archaic spelling; the meaning lives on through 蔑 in 污蔑, while 衊 itself appears only in old texts and etymology notes.
Supplies the sound and reinforces the meaning: 蔑 already carries 'to slight, to disdain', so it doubles as both phonetic and a semantic hint of contempt.