talebearer
An indiscreet person who spreads gossip or blame.
"To speak the truth when my lady commands me," answered the prudential major-domo, "is in some measure my duty, Mistress Lilias; always providing for and excepting those cases in which it cannot be spoken without breeding mischief and inconvenience to myself or my fellow-servants; for the tongue of a tale-bearer breaketh bones as well as Jeddart-staff."
Where it comes from
From Middle English taleberer; equivalent to tale + bearer.
Adapted from the Wiktionary entry talebearer (CC BY-SA 4.0).