pertinacious
Cross references: 1. obstinate per.ti.na.cious \.p*rt-*n-'a--sh*s\ aj [L pertinac-, pertinax, fr. per- thoroughly + tenac-, (Xtenax tenacious, fr. tene-re 1a: adhering resolutely to an opinion, purpose, or design 1b: perversely persistent : OBSTINATE 2: stubbornly unyielding or tenacious : PERSISTENT - per.ti.na.cious.ly av