The exact origin(s) of the word ‘Pernickety’ are lost in the mists of time. In particular, the Scottish mists of time. Clues nevertheless exist. And have been painstakingly investigated by Professor William Sayers, B.A., fil. kand., M.A., Ph.D., of the Medieval Studies Program, College of Arts and Sciences, at Cornell, who notes that :
“In Scotland are found such forms as pirnicky, pernicky, pernicked, pernicket, pernickett, pirnickerie, pernigglety, pick-nickerties, and pernicketies, while in America a major variant appeared (from 1892 onwards) in persnickety and comparable forms.”
Several questions about ‘pernickety’ apparently remain unanswered though :
“How to account for the–s–of the North American form? Can per–again have been sensed as a perfective prefix and–nick-recast as snick ‘a small, quick, and neat cut’, thus a discriminating actor statement?”
See: ‘Pernickety’ by William Sayers, in Scottish Language, 29 (Annual 2010): p87+
Bonus : Professor Sayers has also written extensively on Cant, Rant, Gibberish, and Jargon in ANQ: A Quarterly Journal of Short Articles, Notes and Reviews, Volume 28, 2015 – Issue 1.