Still reading Mason & Dixon, and I’ve hit the following passage:
Below them the lamps were coming on in the Taverns, the wind was shaking the Plantations of bare Trees, the River ceasing to reflect, as it began to absorb, the last light of the Day. They were out in Greenwich Park, walking near Lord Chesterfield’s House,— the Autumn was well advanced, the trees gone to Pen-Strokes and Shadows in crippl’d Plexity, bath’d in the declining light. A keen Wind flow’d about them. Down the Hill-side, light in colors of the Hearth was transmitted by window-panes more and less optickally true. Hounds bark’d in the Forest.
The word “plexity” stopped me cold. It’s not in the OED or the big Webster’s, it’s not from a Latin *plexitas (-plex is only a suffix in Latin) and thus is not a plausible 18th-century formation, and the only modern use of it I can turn up is a sociological one that seems extremely unlikely to be relevant here: “Plexity refers to the type of transactions that we are involved in with other people. If, for example, Tom only ever plays squash with Barbara, the relationship would be considered a uniplex one. If however, Tom and Barbara lived, worked and socialised together it would be a multiplex one.” (From “Language, Society and Power” by Rachael-Anne Knight: .doc file, HTML.) So what’s going on here? Is it simply a nonce abbreviation for complexity, or something more… significant?
Addendum. The word occurs again on p. 505: “Yet aloft, in Map-space, origins, destinations, any Termini, hardly seem to matter,—one can apprehend all at once the entire plexity of possible journeys, set as one is above Distance, above Time itself.”