When I look at the definition given from the Mac OS X Dictionary (I have set American English as interface language, and the dictionary used is then the New Oxford American Dictionary), I read:
the /ði/ /ð(ə)/ /ði/ [called the definite article]
1. denoting one or more people or things already mentioned or assumed to be common knowledge: what's the matter? | call the doctor | the phone rang. Compare with a.
• used to refer to a person, place, or thing that is unique: the Queen | the Mona Lisa | the Nile.
• informal denoting a disease or affliction: I've got the flu.
• (with a unit of time) the present; the current: dish of the day | man of the moment.
• informal used instead of a possessive to refer to someone with whom the speaker or person addressed is associated: I'm meeting the boss | how's the family?
• used with a surname to refer to a family or married couple: the Johnsons were not wealthy.
• used before the surname of the chief of a Scottish or Irish clan: the O'Donoghue.
I have never thought of an article as adjective.
Is normally an article defined as adjective?