Advanced, abstruse, difficult to comprehend; (also) †difficult to perform, arduous (obsolete). In later use frequently with nouns denoting a…

Secret, obscure.

Hard to fathom or ‘get to the bottom of’; penetrating far into a subject, profound.

Of a text, subject, author, etc.: difficult to understand; obscure or unclear in meaning. Now somewhat rare.

Hard, unyielding. Of a question, science, etc.: hard to understand or answer; difficult, impenetrable. Obsolete.

Obscure, veiled from sight or understanding.

Of an immaterial thing: difficult to understand, abstruse; complicated, involved; of the nature of or involving careful discrimination or fine points.

figurative. Not clear to the mind or understanding; obscure, faint.

Of the nature of or involving careful discrimination or fine points; †difficult to understand, abstruse (obsolete); = subtle, adj. 3.

Of words: Of hidden or obscure meaning or reference. Now rare.

Obscure, esoteric, mysterious; = mystical, adj. 2.

Figurative uses. Obscure, hard to understand. Obsolete.

figurative. Darkened or clouded by ignorance, etc.; (of ideas, perception, language) dim, obscure, indistinct; not clear.

Difficult to understand, answer, or explain. Cf. hard word, n. 2.

Obscure, unintelligible; difficult to understand or interpret. Obsolete.

Not easy to understand; not obvious or intelligible.

Difficult to understand, explain, or answer; complex, obscure; confused, vague; doubtful, uncertain. Obsolete.

Difficult to understand; abstruse.

Difficult to understand, obscure; confused; disordered. Cf. diffuse, adj. 1 diffuse, v. 6. Obsolete.

Sought out, ‘recherché’. Of an expedient, explanation, reason: Sought out, ingeniously devised, far-fetched. Of studies: Abstruse.

Of the weather: overcast, cloudy. In extended use: indistinct, obscure.

Not clear or plain to the mind, hard to make out or define; vague, uncertain; enigmatic, ambiguous. Formerly also (Scottish): †unknowable (obsolete).

Concealed, hidden; secret; of concealed or ambiguous meaning. Obsolete.

Of thoughts, conceptions, statements, etc.: Perplexingly involved or complicated in meaning; entangled; obscure.

Not obvious or readily understood; difficult to decide or settle; demanding close consideration; †intricate (obsolete).

Of a person: troubled by deep uncertainty, esp. because of a complicated or unexplained matter; confused, baffled, bewildered, confounded. Of a…

Not easy to understand or solve; = difficult, adj. 1c. Obsolete.

Not easy. Hard to understand, answer, or explain; perplexing; complex, obscure.

Of words: difficult, recondite. Obsolete. rare.

figurative. Having the obscuring, objectionable, or unsubstantial qualities of smoke. Obsolete.

Kept from knowledge or observation; hidden, concealed. Abstruse, recondite; beyond ordinary apprehension or beyond unaided human intelligence. Of…

Difficult to understand; obscure, recondite.

= difficult, adj.

In the senses of the verb: (a) caught or held fast in anything tangled; ensnared; (b) involved in difficulties; embarrassed, perplexed; †(c) (of an…

Discomfited, abashed, put to shame or mental confusion; confused, disordered, etc.: see the verb.

figurative. Of a text, author, etc.: difficult to understand; obscure or unclear in meaning.

Obscure, indefinite, cloudy.

= enigmatic, adj.

= confused, adj. 5.

Of speech, language, etc.: hard to comprehend, obscure, abstruse.

Rendered obscure, dark, or unclear; = obfuscated, adj.

= abstruse, adj.

= abstract, adj. 1.

Said of perceptions or notions in which the elements or parts are mixed up and not clearly distinguished; also of utterance, language, the thinker…

Of doubtful or obscure meaning. Obsolete. rare.

Not evident, not manifest; lacking evidence; not clear or obvious, obscure.

Esp. of a subject of study or discussion: little known or understood; abstruse, obscure; profound.

Not immediately understandable; mysterious, enigmatic.

Darkened; rendered obscure or unclear.

Of an idea or conception: Transcending comprehension; hence, obscure or abstruse. Cf. metaphysical, adj. 1b. Obsolete.

Of or relating to Delphi, a town of ancient Greece on the slope of Mount Parnassus, and to the sanctuary and oracle of Apollo there; hence, of or…

Resembling the ancient oracles in obscurity or ambiguity; = oracular, adj. 1b. Now rare.

Pertaining to, or of the nature of, an enigma, containing or resembling an enigma: ambiguous, obscure, perplexing. Of persons: Mysterious; baffling…

Of a word or idea: recondite, esoteric. Obsolete.

Recondite; abstruse.

(un-, prefix1 affix 2.)

figurative. Involved in obscurity.

Involved in obscurity. Obsolete.

Dim, as if partly blotted out; indistinct, obscure.

Recondite, abstruse. Cf. recherché, adj. Obsolete. rare.

Obscured, indistinct; darkened, clouded over.

Tending or serving to obscure or make dark; obscuring.

figurative. Mentally or morally dark; gloomy; obscure in meaning.

Of or belonging to surpassing depth or profundity.

Abstruse, recondite. Obsolete.

Difficult to understand, obscure; confused; = diffuse, adj. 1. Obsolete.

Of personal attributes, actions, works, etc.: showing depth of insight or knowledge; marked by great learning.

Full of darkness; dark, obscure; gloomy.

Resembling the ancient oracles in mystery, ambiguity, or sententiousness.

Hard to understand; obscure in meaning; not clear or lucid.

(un-, prefix1 affix 4.)

Dark (in various figurative senses); hidden; obscure; unenlightened; unhappy.

Not recognizable; spec. not able to be recognized or identified from previous encounters.

Hard to believe or understand; taxing credulity or comprehension.

= abstruse, adj.

That obscures or darkens; of or belonging to an obscurant; obscurantist.

Unfathomable; immeasurably deep.

That cannot be cleared of clouds or mist, or (figurative) of obscurity; indistinct; inexplicable.

Not obvious, manifest, or evident; not readily perceived or understood.