For an adjective that points to the main or most important thing, your best choice is principal. Is your principal goal for the summer to have fun or to earn some extra money?

The word, principal, comes from the Latin principalis "first in importance" and is related to the title of prince. You can see the relation when you think about its meanings — the head of a school, the starring actor in a film, and the client of an agent. Don't confuse principal with its homophone principle, a moral rule or law of nature. If you talk about a country's principal exports, you mean the main ones.

Primary Meanings of principal

most important element
the educator who has executive authority for a school
(criminal law) any person involved in a criminal offense, regardless of whether the person profits from such involvement
Full Definitions of principal

adj most important element

“the principal rivers of America”
“the principal example”
chief, main, master, primary
important, of import
of great significance or value

n the educator who has executive authority for a school

“she sent unruly pupils to see the principal
head, head teacher, school principal
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the honorary or titular head of a university
headmaster, master, schoolmaster
presiding officer of a school
a woman headmaster
teacher in charge of a school boardinghouse
Type of:
educator, pedagog, pedagogue
someone who educates young people

n the major party to a financial transaction at a stock exchange; buys and sells for his own account

a financial specialist who trades for his own account and so acts both as a broker and principal
Type of:
financier, moneyman
a person skilled in large scale financial transactions

n an actor who plays a principal role

lead, star
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one of two actors who are given equal status as stars in a play or film
film star, movie star
a star who plays leading roles in the cinema
idol, matinee idol
someone who is adored blindly and excessively
TV star, television star
a star in a television show
an object of infatuation
Type of:
actor, histrion, player, role player, thespian
a theatrical performer

n capital as contrasted with the income derived from it

corpus, principal sum
Type of:
wealth in the form of money or property owned by a person or business and human resources of economic value

n the original amount of a debt on which interest is calculated

Type of:
money or goods or services owed by one person to another

n (criminal law) any person involved in a criminal offense, regardless of whether the person profits from such involvement

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Benedict Arnold
United States general and traitor in the American Revolution; in 1780 his plan to surrender West Point to the British was foiled (1741-1801)
William H. Bonney
United States outlaw who was said to have killed 21 men (1859-1881)
John Wilkes Booth
United States actor and assassin of President Lincoln (1838-1865)
Alphonse Capone
United States gangster who terrorized Chicago during prohibition until arrested for tax evasion (1899-1947)
Guy Fawkes
English conspirator who was executed for his role in a plot to blow up James I and the Houses of Parliament (1570-1606)
Jack the Ripper
an unidentified English murderer in the 19th century
Jesse James
United States outlaw who fought as a Confederate soldier and later led a band of outlaws that robbed trains and banks in the West until he was murdered by a member of his own gang (1847-1882)
Robert MacGregor
Scottish clan leader and outlaw who was the subject of a 1817 novel by Sir Walter Scott (1671-1734)
Titus Oates
English conspirator who claimed that there was a Jesuit plot to assassinate Charles II (1649-1705)
Lee Harvey Oswald
United States assassin of President John F. Kennedy (1939-1963)
Jean Laffite
French pirate who aided the United States in the War of 1812 and received an official pardon for his crimes (1780-1826)
Sir Henry Morgan
a Welsh buccaneer who raided Spanish colonies in the West Indies for the English (1635-1688)
Bartholomew Roberts
a Welsh pirate credited with having taken more than 400 ships (1682-1722)
Edward Thatch
an English pirate who operated in the Caribbean and off the Atlantic coast of North America (died in 1718)
Dick Turpin
English highwayman (1706-1739)
Khayr ad-Din
Barbary pirate (died in 1546)
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criminal, crook, felon, malefactor, outlaw
someone who has committed a crime or has been legally convicted of a crime
accessary, accessory
someone who helps another person commit a crime
arsonist, firebug, incendiary
a criminal who illegally sets fire to property
blackmailer, extortioner, extortionist
a criminal who extorts money from someone by threatening to expose embarrassing information about them
bootlegger, moonshiner
someone who makes or sells illegal liquor
briber, suborner
someone who pays (or otherwise incites) you to commit a wrongful act
coconspirator, conspirator, machinator, plotter
a member of a conspiracy
desperado, desperate criminal
a bold outlaw (especially on the American frontier)
fugitive, fugitive from justice
someone who is sought by law officers; someone trying to elude justice
gangster, mobster
a criminal who is a member of gang
a corrupt politician
highjacker, hijacker
someone who uses force to take over a vehicle (especially an airplane) in order to reach an alternative destination
goon, hood, hoodlum, punk, strong-armer, thug, tough, toughie
an aggressive and violent young criminal
gaolbird, jail bird, jailbird
a criminal who has been jailed repeatedly
abductor, kidnaper, kidnapper, snatcher
someone who unlawfully seizes and detains a victim (usually for ransom)
a member of the Mafia crime syndicate in the United States
gangster's moll, gun moll, moll
the girlfriend of a gangster
liquidator, manslayer, murderer
a criminal who commits homicide (who performs the unlawful premeditated killing of another human being)
parolee, probationer
someone released on probation or on parole
drug dealer, drug peddler, drug trafficker, peddler, pusher
an unlicensed dealer in illegal drugs
someone who commits crimes for profit (especially one who obtains money by fraud or extortion)
raper, rapist
someone who forces another to have sexual intercourse
habitual criminal, recidivist, repeater
someone who is repeatedly arrested for criminal behavior (especially for the same criminal behavior)
one who habitually ignores the law and does not answer court summonses
contrabandist, moon curser, moon-curser, runner, smuggler
someone who imports or exports without paying duties
stealer, thief
a criminal who takes property belonging to someone else with the intention of keeping it or selling it
traitor, treasonist
someone who betrays his country by committing treason
law offender, lawbreaker, violator
someone who violates the law
Type of:
offender, wrongdoer
a person who transgresses moral or civil law

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