Irredentist

Meaning: with a lower-case i, someone who advocates seizing territory back* from another nation or state. With a capital, a member of a 19th century Italian political party which advocated the annexation of Italian-speaking districts from surrounding nations.

Usefulness: 2 (Slightly abstruse, but you'll get points from the politically inclined. Could be useful if you were interviewing Diego Marani, who likes to discuss the attempts of nation-states to co-opt language as identity and/or delineator of borders, and the way that the EU is - possibly - undoing that. Podcast here, or interview here. He's also attempted a universal language, albeit a Euro-centric one.)

Logofascination: 2 (From the Italian for 'unredeemed', as in 'unredeemed Italy'.)

In the wild: A Washington Post blogpost on the issues with a study that supposedly mapped 'racial tolerance'.

Vocitated

Meaning: named or called.

Usefulness: 2 (It strikes me as a satisfyingly annoying way to ask someone's name "And what are you vocitated, old chap?" or introduce yourself: "I am occasionally vocitated as The Antipodean.")

Logofascination: 1 (The English version was invented by Sir Thomas, who is the sole citation in the OED.)

In the wild: Occasionally; someone's already taken it as a Twitter handle, worse luck.

Stentoriphonically

Meaning: loudly; as if through a speaking-trumpet, or stentorophonic horn.

Usefulness: 2 (It's a bit of a mouthful, but useful if you're after something elaborate. Stentorophonic horn is rather useful as a more interesting name for hearing aids.)

Logofascination: 1 (In 1671 Sir Samuel Morland - academic, diplomat, spy, inventor and mathematician* - claims to have invented what we would call a megaphone, but he called the stentorophonic horn. Stentoriphonically appears in G&P Le Tiers-Livre in 1693, but Sir Thomas had died in 1660; this may be one of Motteux's sneaking in. Sir Thomas might well have made an allusion to Stentor, mythical source for this and stentorian, but the suffix -phonic is not quite right.**)

In the wild: No.

Mezentian

Meaning: resembling Mezentius, an Etruscan king exiled for cruelty (according to Virgil, anyway).

Usefulness: 1 ("An early meeting the day after a long weekend? A Mezentian idea!")

Logofascination: 1 (The OED has three citations between 1798 and 1874. The next is 1992, from Iain Banks' Crow Road. Between Iain and Iain M. Banks, the late, lamented author has 136 citations in the OED, a number of them to do with whisky. Sadly, my favourite of his books, Transition,  seems to have been lexicographically neglected by the OED. If you're interested, the list of the words with Iain / Iain M. Banks citations is at the end of the post.)

In the wild: Crow Road: "It did occur to me he could have driven the bike himself with the body lashed to his back looking like a pillion. It's a bit Mezentian, but possible."

Myki

Meaning: Old Norse for cow dung. No, really. See also here.

Usefulness: 1. (Google tells me that there was a bit of press about this when the system first came out, but no-one told me.)

Logofascination: 1 (Etymologically related to muck and midden.  Mainly of interest to those of us residing in Melbourne; myki is our public transport ticketing system. Its problems are so notorious that there's a hashtag: #mykifail. I suppose it provides the rest of you with a usefully obscure word for cow dung; "This report is sheer myki!")

In the wild: Of all places, I found it in a post on Lancashire dialect. I'm trying to figure out where loomster comes from.

Degrees: 3

Connections: myki - muck - manurers (It's been a while since we had a word this far removed; I think this is because Sir Thomas used Scottish vernacular rather than English - muck and midden - and the influences are different.)

Which is used in: Logopandecteision. To over-simplify, Sir Thomas is arguing that you can verify how ancient his heritage is by considering that of his tenants:

both historie and the most authentick tradition we have, avoucheth the first labourers and manurers of the land to have come along with my ancestors Beltistos, Nomostor, and Lutork, and for their good service done, especially to the last of those three, received leases thereupon in the quality of yeomans, who were so well pleased with what they got that after they had most contentedly spent the best of their age, when decrepit years did summon them to pay their last due to nature, they bequeathed unto their children the hereditarie obedience they did owe their master, to whom they left their blessing and best wishes 

Manure originally just meant cultivate, but of course manuring is one of the chief activities of cultivation, particularly before modern fertilizers. 

Penitissim

Meaning: Innermost.

Usefulness: 2 (Could lead to some confusion if used carefully, which Rabelais might have been counting on.)

Logofascination: 1 (Originating in Pantagruel, this is probably a Rabelaisian coinage, although it's from a common enough Latin root, penitus. The OED has Sir Thomas' Ekskybalauron as the sole citation, since it is the main English source. I can't help but wonder if it's in the OED to help explicate Rabelais, much as most of Cotgrave exists for that purpose.

The really fascinating thing about this word, though, is that Ekskybalauron was published before Sir Thomas' Rabelais translation - they are only a year apart, but this suggests that he was already working on the translation, and had thought about how to Anglicise this passage.)

In the wild: Besides the piece on neologism I linked to recently, it's also cited in a rather useful dissection of the original.