Poorly stated or described:
— He confuses the reader with ill-defined terms and concepts.

synonym: unclear.

Roget 447: invisible, imperceptible; undiscernible^†, indiscernible; unapparent, non-apparent; out of sight, not in sight; a perte de vue [Fr.]; behind the scenes, behind the curtain; viewless, sightless; inconspicuous, unconspicuous^†; unseen etc. (see) etc. 441; covert etc. (latent) 526; eclipsed, under an eclipse.    dim etc. (faint) 422; mysterious, dark, obscure, confused; indistinct, indistinguishable; shadowy, indefinite, undefined; ill-defined, ill-marked; blurred, fuzzy, out of focus; misty etc. (opaque) 426; delitescent^†.    hidden, obscured, covered, veiled (concealed) 528.    ... show more