There is an entire field looking at this question called "Computational Linguistics". Looking at any online translation tool you can see that they still have a ways to go, but there has been a lot done on parsing English.
Stanford provides a robust English parser here with the homepage here.
I recommend using an established library for your script rather than writing your own. There is no reason to reinvent the wheel, especially a wheel that contains the complications of the English language.
It's the same reason dictionaries don't usually explicitly list standard plurals, verb inflections, etc.
In the case of plasticity, for example, the base word plastic has multiple "shades" of meaning. Without the definition, you might think perhaps it meant the proportion of plastic incorporated in a composite material. Okay, not likely, but you get my drift.
In the case of hermetic, it doesn't really matter if you don't know which precise meaning is embodied in hermeticity (so far as I'm aware, effectively they all are). Occam's razor and all that.
It's not all that common, and anyone reading it who doesn't recognise the word couldn't fail to discover an entry for hermetic if they check any dictionary. They'll figure it out.
It's also worth copying in this from OED
2 b. hermetic seal, hermetic sealing: air tight closure of a vessel, esp. a glass vessel, by fusion, soldering, or welding; also applied in Surg. to a method of dressing wounds (see quot. 1886).
Also fig. Hence hermetic for ‘hermetically sealed’. [emphasis mine]
That's one of about a dozen definitions for hermetic in the OED entry, and all the rest relate closely to the original literal pertaining to Hermes Trismegistus, and the ... writings ascribed to him.
From which I conclude that standalone adjectival hermetic in OP's sense is probably relatively new, and the extrapolation from this to an abstract noun for quality of being hermetic even newer. Perhaps the dictionaries just haven't caught up yet.
Best Answer
Each iteration is correct here.
Iterate as a noun means the end result of many iterations. So in an iterative function, each iteration is one loop of calculation, whereas the iterate is the sum of all iterations performed.
An important thing to note here is that iterate can also mean a function that iterates. So if you ever see the noun iterate used, test both definitions to see which makes more sense.