Definition of pertinacious adjective from the Oxford Advanced Learner's Dictionary

 

pertinacious

 adjective
adjective
BrE BrE//ˌpɜːtɪˈneɪʃəs//
 
; NAmE NAmE//ˌpɜːrtnˈeɪʃəs//
 
(formal)
 
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determined to achieve a particular aim despite difficulties or opposition Word Origin early 17th cent.: from Latin pertinax, pertinac- ‘holding fast’ + -ous.
See the Oxford Advanced American Dictionary entry: pertinacious