What does "mizzy" mean?

Mizzy: A bog or quagmire. [Obs.] Ainsworth. M'-NAUGHT M'-Naught" (mak*nalt"), v. t. (Steam Engines) To increase the power of (a single-cylinder beam engine) by adding a small high-pressure cylinder with a piston acting on the beam between the center and the flywheel end, using high-pressure steam and working as a compound engine, -- a plan introduced by M'Naught, a Scottish engineer, in 1845.

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