subject

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

• adjective Being in a position or in circumstances that place one under the power or authority of another or others.
• adjective Prone; disposed.
• adjective Likely to incur or receive; exposed.
• adjective Contingent or dependent.
• noun One who is under the rule of another or others, especially one who owes allegiance to a government or ruler.
• noun One concerning which something is said or done; a person or thing being discussed or dealt with.
• noun Something that is treated or indicated in a work of art.
• noun Music A theme of a composition, especially a fugue.
• noun A course or area of study.
• noun A basis for action; a cause.
• noun One that experiences or is subjected to something.
• noun A person or animal that is the object of medical or scientific study.
• noun A corpse intended for anatomical study and dissection.
• noun One who is under surveillance.
• noun Grammar The noun, noun phrase, or pronoun in a sentence or clause that denotes the doer of the action or what is described by the predicate.
• noun Logic The term of a proposition about which something is affirmed or denied.
• noun The essential nature or substance of something as distinguished from its attributes.
• noun The mind or thinking part as distinguished from the object of thought.
• transitive verb To cause to experience, undergo, or be acted upon.
• transitive verb To subjugate; subdue.
• transitive verb To submit to the authority of.

from The Century Dictionary.

• To put, lay, or spread under; make subjacent.
• To expose; make liable or obnoxious: with to: as, credulity subjects one to impositions.
• To submit; make accountable, subservient, or the like; cause to undergo; expose, as in chemical or other operations: with to: as, to subject clay to a white heat.
• To bring under power, dominion, or sway; subdue; subordinate.
• To be or become subject.
• noun In geometry, the figure cut by the picture-plane.
• noun In experimental psychology: The observer or reactor; the person upon whom an experiment is made.
• noun More correctly, the person, normal or abnormal in mental condition, who is subjected to a mental test or an examination of mental efficiency.
• Placed or situated under or beneath.
• Being under the power or dominion of another.
• Exposed; liable, from extraneous or inherent causes; prone: with to: as, a country subject to extreme heat or cold; a person subject to attacks of fever.
• Hence Exposed or liable, as to what may confirm or modify: with to: as, subject to your approval; subject to correction.
• Submissive; obedient.
• Synonyms Subordinate, subservient, inferior.
• Apt, Likely, etc. See apt.
• noun One who is placed under the authority, dominion, or controlling influence of another; specifically, one who owes allegiance to a sovereign and is governed by his laws; one who lives under the protection of, and owes allegiance to, a government.
• noun A person or thing regarded as the recipient of certain treatment; one who or that which is exposed or liable to something specified.
• noun Specifically— A dead body used for dissection.
• noun One who is peculiarly sensitive to psychological experimentation; a sensitive.
• noun One who or that which is the cause or occasion of something.
• noun That on which any mental operation is performed; that which is thought, spoken, or treated of: as, a subject of discussion or negotiation; a subject for a sermon or a song; the subject of a story.
• noun In grammar, that of which anything is affirmed; the nominative of a verb, without or with modifiers; the member or part of a sentence signifying that of which predication is made.
• noun In logic, that term of a proposition of which the other is affirmed or denied.
• noun In metaphysics: A real thing to which given characters relate and in which they are said to inhere.
• noun In Kantian and modern philosophy, the self or ego to which in all thought all mental representations are attributed (according to Kant); also, a real (hypothetical) thing in which mental phenomena are supposed to inhere.
• noun In music: In general, the theme or melodic phrase on which a work or movement is based, consisting of few or many tones variously combined and treated; a motive. When two or more principal subjects are used, they are often known as first, second, etc.