Gossip
Sagacious confidence
**Sagacious** means wise or shrewd—Dickinson's making gossip sound like serious intelligence work, not idle chatter.
Portentous inference
**Portentous** means ominous or prophetic. The gossipers think they're reading important signs, making dramatic deductions from small clues.
Enjoining secrecy
**Enjoin** means to command or urge strongly—both leaves and women insist on confidentiality even as they spread information.
Inviolable compact / To notoriety
The paradox lands here: an **inviolable** (unbreakable) promise of secrecy that leads directly **to notoriety** (public knowledge). The secret-keeping is the spreading.