What's the "een" in Halloween?
early 15c., opake, from Latin opacus "shaded, in the shade, shady, dark, darkened, obscure," of unknown origin. Spelling influenced after c.1650 by French opaque (c.1500), from the Latin. Figurative use from 1761. Related: Opaquely; opaqueness.
opaque o·paque (ō-pāk')
Impenetrable by light; neither transparent nor translucent.
Resistant to the transmission of certain kinds of radiation, usually light. Metals and many minerals are opaque to light, while being transparent to radio waves and neutrinos. Compare translucent, transparent.