These words refer to things kept secret or hidden or to things difficult to perceive or understand. Obscure is the most general and least formal of these; it is now most often used to indicate things indistinct or difficult to grasp, although it still may reflect its derivation from a root meaning dark.

• The letters of the sign were made obscure by rain; obscure , involuted reasoning that only served to confuse his audience; a path that grew more and more obscure in the fading light.

When the reference is to understanding, the word may imply disapproval because something is not clear: misled by the deliberately obscure language of the contract. The word may refer with greater neutrality to something that is not clear. Without necessarily implying any intent to confuse: references that were perfectly apparent in his own time but that have long since become obscure .

Cryptic and arcane specifically stress things that are hidden or that have been deliberately made remote from easy understanding. Arcane can flatly refer to something kept secret as a mystery: arcane religious symbols that only the high priest could interpret. More generally, it may refer to a purposely pedantic reliance on obscure references in order to show off one’s own learning; in this sense, the word, like obscure , can carry a disapproving tone: arcane footnotes that not even a specialist in the field could be expected to understand. Cryptic may refer to the occult, but more generally it indicates something enigmatic or puzzling, often something deliberately made to seem meaningless, except to the initiated: cryptic signs and handclasps that were part of the lodge’s ritual. The word may also refer to something too brief to be understood: a cryptic , one-word clue.

Abstruse and recondite may refer to things secret, hidden or difficult to grasp, but their special area of usage here is in referring to scholarly complexity. Abstruse suggests a formal or learned style filled with difficulties that tax the mind: abstruse legal documents that supported his claim. Recondite is even more emphatic about the difficulty or complexity of a study or approach: needing fewer recondite books on the subject and more that might help a layman to understand the new discoveries. Hence, by extension, the word can refer to knowledge remote from the mainstream and available only to a few authorities: the recondite teachings of a minor medieval philosopher.