Q: What's the meaning of "finniky"? There is this sentence in a letter of Bertrand Russell:

Even the absurdities - the thunder and lightning - are big and invigorating after the stifling finniky appropriateness of everything French.

I couldn't find this anywhere. Is it a typo? The following words have similar spelling : finicky, Finnic, finicking (also finikin, finnicking, finnikin). 

A: In the seventeenth and eighteenth centuries—and indeed until World War I, the dominant form of the word that we now know as finicky was finical. Here is an Ngram chart of the variants finical (yellow line) versus finicky (red line) versus finnicky (blue line) versus finiky (green line) versus finniky (no line) for the years 1785–2005:

The reason the spelling finniky has no line in this chart is that Google reports "Ngrams not found" for that spelling—an announcement that it makes when the Google Books matches for a particular spelling fall below some threshold number. Nevertheless, a Google Books search for finniky turns up close to 80 matches, going back to the first half of the nineteenth century.  
One interesting early instance is this one from John Brockett, A Glossary of North Country Words, in Use (1825):

FINNIKING, FINNIKY, trifling, scrupulously particular. Perhaps variations of finical.

The third edition of Brockett, A Glossary of North Country Words, with Their Ethymology, and Affinity to Other Languages (1846) dispenses with finniking but sticks with finniky and loses any doubt about the connection to finical:

FINNIKY, trifling, scrupulously particular—finical. 

Another dictionary notice occurs in James Donald, Chambers's English Dictionary: Pronouncing, Explanatory, and Etymological (1872), which curiously enough lists it in what amounts to an appendix of "Americanisms":

Finnikin, Finniking, Finniky, finical.

The spelling finniky continues to appear sporadically in English publications until at least 1928, after which the possibility that occurrences are simply typos becomes more likely, as the spelling finicky becomes more and more dominant.
Russell's use of finniky occurs in a letter to Alys Pearsall Smith dated "1–2 October 1894 midnight" and is reprinted in The Selected Letters of Bertrand Russell: The Private Years, 1884–1914 (1992). The years 1884–1914 are roughly the period when finicky went from a very low frequency of occurrence to a frequency almost equal to that of finical, and 1894 is well within the era when finniky still occasionally appeared in print as an acceptable variant form.
