If you call your teacher a "dirty toad," you're going to get into trouble––she'll call you out on the slander. Slander is the act of making a false, negative spoken statement about someone.
In law, the word slander is contrasted with libel, which is the act of making a false written statement about someone. The noun slander is from Old French esclandre, escandle "scandal," from Late Latin scandalum "stumbling block, offense."
n words falsely spoken that damage the reputation of another
v charge falsely or with malicious intent; attack the good name and reputation of someone
destroy or damage seriously, as of someone's reputation
print slanderous statements against
badmouth, drag through the mud, malign, traduce
speak unfavorably about