English: morass

Tutoring English, words can return. The tutor recalls the word morass.

morass: an impairment to motion or mental clarity, akin to a swamp one would try to traverse.

I first heard morass decades ago, and hear it rarely now.

Source:

Mish, Frederick C. (editor). The Merriam-Webster Dictionary. Springfield: Merriam-Webster, 2004.