Opacous

The firm opacous Globe / Of this round World, whose first convex divides / The luminous inferior Orbs.

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And vve particularly remember, that, being at ſome diſtance from London one Night, that the People, upon a very vvell-come Occaſion, teſtified their Joy by numerous Bon-fires; though, by reaſon of the Interpoſition of the Houſes, vve could not ſee the Fires themſelves, yet vve could plainly ſee the Air all enlighten'd over and near the City; vvhich argu'd, that the lucid Beams ſhot upvvards from the Fires, met in the Air with the Corpuſcles opacous enough to reflect them to our Eyes.

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[I]f you take ammel that is almost opacous, and grind it very well on a Porphyry, or Serpentine, the small particles will by reason of their flaws, appear perfectly opacous […]

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The upper wings are opacous; at their hinder ends, where they lap over, transparent, like the wing of a fly.

Source: wiktionary