Difficult to understand
Else clues• Abstruse
• Arcane
• Enigmatic
• For initiates only
• Incomprehensible
• Indecipherable
• Inscrutable
• Intended for a select few
• Just for a few
• Known by few
• Known only to insiders
• Like the in-group
• Like trivia
• Limited-appeal
• Mysterious
• Not clear to most
• Not for everyone
• Not for the masses
• Not widely known
• Obscure
• Odd, as a range of knowledge
• Only for certain tastes
• Puzzling
• Rarefied
• Recondite
• Secret
• Shrouded in mystery
• Understood by a few
• Understood by a select few
• Way out there
• Way-out