The OED does have “plex, n. Obs. rare. A plait or braid (of hair).”, with one 15th‐c. attestation. Pynchon may have come across that or, more likely, been thinking of the general word family of Latin plectere, suggesting how the branches of the trees were intertwined.

S.

There's no reason it couldn't be a word in its own right, even if it's not attested in Latin. Some suffixes had their vowels changed by Old Latin stress, but -plex comes from a stem plex-, supine of plect-, so **plexitas should be a perfectly good word for 'plaitedness'.

When I first read this my innards said perplexity, possibly complexity.

If you try the A9 search on amazon.com and ignore the many compounds then it seems to exist as a word in its own right in at least three contexts.

History and etymology I'll leave to you!

Perhaps "plexity" is just a typo? "Pexity" might even make some sense in the context.

"Plexity" looks a bit like "arity". indeed it is used in communications to describe the underlying concept of simplex/half-duplex/full-duplex connections.

There seems to be some other modern usages, for example:

When we study nominal expressions, a basic distinction must be made
between nouns, which are linguistic entities, and their referents, which are
mental entities (Karttunen 1976). The mental entities involved in this discus-
sion will be described with the help of two of Talmy’s (1988) four categories for
noun referents: ‘dimension’, ‘plexity’, ‘boundedness’ and ‘dividedness’. These
terms thus deal with semantic-conceptual entities, not syntactic categories. The
semantic-conceptual characteristics, however, do interact with their syntactic
encoding, as we will see in the second part, where I propose that the bare plural
is motivated by the formal properties of mass nouns. The two categories used in
this paper are plexity and boundedness.
Plexity has to do with “a quantity’s state of articulation into equivalent
elements” (ibid.: 176). When a quantity consists of only one of its ‘atoms’, it is
‘uniplex’ (‘a cat’), and when it consists of several instances of one atom, it is
‘multiplex’ (‘cats’). This distinction corresponds to the linguistic category of
number, with singular and plural nouns.

from http://www.benjamins.nl/jbp/series/LiC/3-2/art/val.pdf

from a google search, which yields quite a few answers:
http://www.google.com/search?hl=sv&c2coff=1&q=plexity+-%22com+plexity%22+-%22complexity%22&btnG=S%C3%B6k&lr=

I also remember that the word "plexity" is used in a quite specific sense (though difficult to explain) in Samuel R Delany's sf-novella "Empire star".

Stefan: I'm tentatively adopting that as my reading, since it makes sense of the formation and the context.

Malte: I'm aware of the uses you refer to, but discarded them as possible influences on Pynchon -- too specialized and remote in meaning.

knowing Pynchon, he intended the obscure sociological meaning for his metaphor.

anachronistic only for the erudite--& this, too, is an effect.

m.

Oh. I didn't think ANYTHING would be too specialized and remote in meaning when it comes to Pynchon...

True in theory, but what sense would the sociological reading make here?

Yes, you're right, of course. Incidentally, I look'd up the Passage in the Swedish Translation, lodged next to the English Original in my crowded Book-Shelf, and it seems that this curious Plexity left the (very good) Translator quite perplex'd.

So how does the Swedish translator deal with the pastiche of 18th-century style? Were random capitalizations part of Swedish as well?

Yes, they were. As was the hyphen-use. However, the Swedish 18th century was also very influenced by French languange and literature, and the translator accordingly adopts lots of French loanwords and variants of spelling. Syntactically he makes a compromise between Pynchons long Sternian (?) sentences and the more compact style typical of Swedish prose of the same period.

I know this is offbeat, but... When I came in to work this morning, the department secretary had put on my desk a package of beautiful wool felting yarn that I ordered from Uruguay. I had it in my hands, thinking about the knitting project I was going to make with it, when I was reading the post above. My mind immediately made a connection "plex = ply," and the braided, interlaced tree shadows merged in my mind's eye with some failed attempts at pen-and-ink Celtic knotwork I'd previously attempted. "Plexity" seemed like perfectly clear and understandable English. "Complexity" would certainly not have been the correct choice, and "perplexity" would have been even, uh, wronger. :)

Yes, I think you're right -- it's basically the same idea Stefan had (first comment), and I'm a bit abashed I didn't think of it myself. My Latinity is a tad rusty.

Mason & Dixon sounds like nonsense - a very weak and ill-informed pastiche at best. Where in Greenwich Park are you anywhere near a 'forest'? Why would hounds bark there, and not dogs? The omission of 'e' in preterites (flow'd, etc.), although very Georgian, looks somehow wrong here as well, though I can't be bothered to find out why. Plexity is the least of your worries.

What are the chances that within a week of your posting this, I'd come across the word in unrelated reading? Pretty low, I'd say. Yet there it is in Leonard Talmy's Toward a Cognitive Semantics. The sense is similar to the sociological one, in that it's the difference between uniplex and multiplex. It's a schematic category within the schematic system of configurational structure, if I'm getting Talmy's terminology right.

The category here to be termed plexity is a quantity's state of articulation into equivalent elements. Where the quantity consists of only one such element, it is uniplex, and where it consists of more than one, it is multiplex. When the quantity involved is matter, plexity is, of course, equivalent to the traditional linguistic category of "number" with its component notions 'singular' and 'plural'. But the present notions are intended to capture the generalization from matter over to action, which the traditional terms do not do. It is true that there are the traditional terms "semelfactive" and "iterative" referring, respectively, to one and more than one instantiation of an event. But there is no real temporal equivalent to "number." "Aspect" includes too much else about the temporal structure of action. And in any case, none of the traditional terms refers generically to both the spatial and temporal domains.

As indeed it does!

A belated comment: Plexity sounds like one of those invented names for corporations that sound like they should be words, but aren't, like Agilent, Accenture, Viant and Scient (all real). "Plexity -- we help you make chaos out of order." By the way, www.plexity.com is for sale for $2,200.

I found a definition for plex, "Refers to the number of sides imaged." So plexity is a noun form of the same?