What words rank the highest on Dictionary.com's difficulty index?

While the sources provided do not specifically mention Dictionary.com's difficulty index, they do list several complex and less commonly used English words that are generally considered difficult. Here are some examples from these sources:

From the ACT Vocabulary List

• Capricious: Unpredictable; impulsive1.
• Chicanery: Deceitful trickery or cheating1.
• Concomitant: Accompanying or associated with something else; existing at the same time1.
• Conundrum: A difficult problem or question1.
• Deleterious: Harmful; damaging1.
• Maladroit: Clumsy or awkward in movement or behavior1.
• Mawkish: Excessively sentimental; sappy1.
• Reprehensible: Deserving criticism or condemnation1.

From the List of Difficult English Words

• Byzantine: Complex and intricate2.
• Consanguineous: Of the same blood or origin (descended from the same ancestor)2.
• Demagogue: A political leader who uses rhetoric to appeal to prejudices and desires of ordinary citizens2.
• Inchoate: Only partly in existence; imperfectly formed2.
• Invective: Abusive language2.
• Pulchritudinous: Physically beautiful2.
• Truculent: Having a fierce, savage nature2.
• Vicissitude: An unwelcome or unpleasant change in circumstances or fortune2.

From Moira Rose's Vocabulary on Schitt's Creek

• Balatron: A buffoon; one who speaks a lot of nonsense and is characterized by self-indulgence2.
• Confabulate: To hold an informal discussion2.
• Omphaloskepsis: A lack of will to move, exert, or change2.
• Panache: Distinctive and stylish elegance2.
• Polyphiloprogenitive: Extremely prolific; tending to produce offspring, or characterized by love of offspring2.

These words are selected for their complexity, rarity, and the likelihood that they would be challenging for many people to understand and use correctly.