abstruse
1. [ adjective ] difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge
Synonyms: recondite deep
Examples:

"the professor's lectures were so abstruse that students tended to avoid them" "a deep metaphysical theory" "some recondite problem in historiography"

Related terms: esoteric
Similar spelling:   abstrusely
  abstrusity
  abstracter
  abstracted
  abstractor
  abused
  abstract