obstinate

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Stubbornly adhering to an attitude, opinion, or course of action; obdurate.
• adjective Characterized by such adherence.
• adjective Difficult to manage, control, or treat.

from The Century Dictionary.

• Pertinaciously adhering to an opinion, purpose, or course of action; not yielding to argument, persuasion, or entreaty; headstrong.
• Springing from or indicating obstinacy.
• Not easily controlled or removed; unyielding to treatment: as, an obstinate cough; an obstinate headache.
• Synonyms Obstinate, Stubborn, Intractable, Refractory, Contumacious, pertinacious, headstrong, unyielding, dogged, wilful, persistent, immovable, inflexible, firm, resolute. The first five words now imply a strong and vicious or disobedient refusal to yield, a resolute or unmanageable standing upon one's own will. Stubborn is strictly negative: a stubborn child will not listen to advice or commands, but perhaps has no definite purpose of his own. Obstinate is active: the obstinate man will carry out his intention in spite of advice, remonstrance, appeals, or force. The last three of the italicized words imply disobedience to proper authority. Intractable, literally not to be drawn, handled, or governed, is negative; so is refractory: both suggest sullenness or perverseness; refractory is more appropriate where resistance is physical: hence the extension of the word to apply to metals. Contumacious combines pride, haughtiness, or insolence with disobedience; in law it means wilfully disobedient to the orders of a court.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Pertinaciously adhering to an opinion, purpose, or course; persistent; not yielding to reason, arguments, or other means; stubborn; pertinacious; -- usually implying unreasonableness.
• adjective Not yielding; not easily subdued or removed

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Stubbornly adhering to an opinion, purpose, or course, usually with implied unreasonableness; persistent.
• adjective Said of inanimate things not easily subdued or removed.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective resistant to guidance or discipline
• adjective stubbornly persistent in wrongdoing
• verb persist stubbornly
• adjective tenaciously unwilling or marked by tenacious unwillingness to yield