the thing that is being discussed, considered, or studied:
an area of knowledge that is studied in school, college, or university:
to start talking about a different subject:
a person, thing, or situation that is written about in a book, article, etc. or shown in a picture, etc.:
the person or thing that performs the action of a verb, or is joined to a description by a verb:
a person who lives in or who has the right to live in a particular country, especially a country with a king or queen: