addict

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

• transitive verb To cause to be physiologically or psychologically dependent.
• transitive verb To occupy (oneself) with or involve (oneself) in something habitually.
• transitive verb To cause to use something on a regular or dependent basis.
• noun One who is addicted, as to narcotics or gambling.
• noun A devoted adherent; a fan.

from The Century Dictionary.

• To devote or give up, as to a habit or occupation; apply habitually or sedulously, as to a practice or habit: used reflexively: as, to addict one's self to the exercise of charity; he is addicted (addicts himself) to meditation, pleasure, or intemperance.
• To give over or surrender; devote, attach, or assign; yield up, as to the service, use, or control of: used both of persons and of things.
• Specifically In Roman law, to deliver over formally by the sentence of a judge, as a debtor to the service of his creditor.
• Addicted.

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

• past participle obsolete Addicted; devoted.
• transitive verb To apply habitually; to devote; to habituate; -- with to.
• transitive verb obsolete To adapt; to make suitable; to fit.

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

• noun A person who is addicted, especially to a harmful drug
• noun An adherent or fan (of something)
• verb To cause someone to become addicted, especially to a harmful drug
• verb To involve oneself in something habitually, to the exclusion of almost anything else.
• verb obsolete To adapt; to make suitable; to fit.

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

• verb to cause (someone or oneself) to become dependent (on something, especially a narcotic drug)
• noun someone who is physiologically dependent on a substance; abrupt deprivation of the substance produces withdrawal symptoms
• noun someone who is so ardently devoted to something that it resembles an addiction