What is the pronunciation of "liceity"?

Solution 1:

I’m not convinced that it’s a valid word, because the -eity suffix denotes “a noun of quality or condition corresponding to adjectives in -eous suffix” [OED]. Liceous for licit is at best doubtful.

However, in the absence of authoritative data such as the OED might provide, it would be reasonable to assign a pronunciation based on other -eity words. In these (at least in British English) the -e- is stressed, the preceding syllable is unstressed and possibly reduced, and the pronunciation might therefore be presumed to be /liˈseɨti/.

Pronouncing an unusual word in a reasonably standard way may help the hearer to spell it and thereby to understand it: /liˈseɨti/ is likely to be spelled liceity; the lic- part is probably to do with law and the -eity part denotes a “noun of condition” and thus the word may be presumed to mean lawfulness.

Footnote: Documents of the Roman Catholic Church are always published in Latin first and then translated, so it’s entirely possible that a standard Latin word for licitness — such as liceitatem — has been clumsily translated as liceity.