ill-defined shadow

Standing by the ruins of Urquhart castle, with rolling thunder clouds shadowing the lake's ruffled waters, the visitor to Loch Ness is primed to see the monster in any ill-defined shadow or indeterminate movement.

She could see through an open door to a landing across which light and ill-defined shadows of banisters lay, to a corner of wall; the continuation of landing had to be deduced from the chiaroscuro eclipsed by the bedroom doorpost.