Definition of pertinacious adjective from the Oxford Advanced American Dictionary

 

pertinacious

 adjective
adjective
NAmE//ˌpərtnˈeɪʃəs//
 
(formal)
 
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determined to achieve a particular aim despite difficulties or opposition
pertinacity
 
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NAmE//ˌpərtnˈæsət̮i//
 
noun [uncountable] With his usual pertinacity, he pursued this new line of inquiry.
See the Oxford Advanced Learner's Dictionary entry: pertinacious