- holding tenaciously to a purpose, course of action, or opinion; resolute.
- stubborn or obstinate.
- extremely or objectionably persistent.
- pertaining or relating directly and significantly to the matter at hand; relevant.
I can't find anything in common in terms of their meaning. Although,
Pertinent:from Latin pertinēns, from pertinēre to pertain
Pertinacious:1620-30; pertinaci(ty) + -ous
And pertinent is related to pertinence, which looks similar to pertinacious. Is it a coincidence?
Let me know if these questions are not constructive, I'll stop posting. By the way, I'm studying vocabulary for English test so I'm trying to find a way to memorize words that look similar otherwise I'll have to do it all by rote.