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

Figurative uses. Obscure, hard to understand. Obsolete.

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

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

Not easy to understand; not obvious or intelligible.

Stopped, obstructed. Also (figurative): impervious.

Of words, statements, explanations, etc.: difficult to understand; not clearly expressed. Also, of a person, esp. a writer: difficult to understand…

Not plain (in various senses); esp. ornate, elaborate; (also) uneven; rough. In early use: insincere, false (see plain, adj.2 11).

Obscure.

Difficult to understand; obscure, recondite.

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

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

= abstruse, adj.

Of writing, speech, thought, etc.: obscure, vague; confused, illogical; badly expressed.

Not perspicuous; esp. not easily seen or understood; obscure, opaque, unclear.

figurative. Involved in obscurity.

Not clearly expressed or easily understood; obscure, opaque; (of a speaker or writer) unclear in style, meaning, or expression. Occasionally also…

Difficult to make out, understand, or decipher; crabbed.

Not lucid (in various senses); esp. unintelligible, obscure.

Difficult to understand; abstruse.

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

Having the quality of obscuring or darkening.

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

figurative. Sluggish, tedious; confused and undefined, ‘muddy’.