pertinacious

Holding tenaciously or stubbornly to a purpose, opinion, or course of action.

Extremely persistent or unyielding.

Unyielding; persistent; obstinate; especially, resolute, as in holding or adhering to an opinion, purpose, design, course of action, etc.

Synonyms Unyielding, dogged: the word is rarely used now except in condemnation. See obstinate.

Holding or adhering to any opinion, purpose, or design, with obstinacy; perversely persistent; obstinate.