upstart

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A person of humble origin who attains sudden wealth, power, or importance, especially one made immodest or presumptuous by the change; a parvenu.
2. adj. Suddenly raised to a position of consequence.
3. adj. Self-important; presumptuous.
4. v. To spring or start up suddenly.

Century Dictionary and Cyclopedia

1. To start or spring up suddenly.
2. n. One who or that which starts or springs up suddenly; specifically, a person who suddenly rises from a humble position to wealth, power, or consequence; a parvenu.
3. n. One who assumes a lofty or arrogant tone.
4. n. A puddle made by the hoofs of horses in clayey ground. Halliwell. The meadow-saffron, Colchicum autumnale, whose flowers spring up suddenly without leaves.
5. Starting up suddenly; quickly rising.
6. Suddenly raised to prominence or consequence; parvenu: as, “a race of upstart creatures,”
7. Characteristic of a parvenu; new and pretentious.

Wiktionary

1. n. One who has suddenly gained wealth, power, or other prominence, but either has not received social acceptance or has become arrogant or presumptuous.
2. adj. self-important and presumptuous
3. v. to rise suddenly, to spring

GNU Webster's 1913

1. v. To start or spring up suddenly.
2. n. One who has risen suddenly, as from low life to wealth, power, or honor; a parvenu.
3. n. (Bot.) The meadow saffron.
4. adj. Suddenly raised to prominence or consequence.

WordNet 3.0

1. n. an arrogant or presumptuous person
2. n. a gymnastic exercise performed starting from a position with the legs over the upper body and moving to an erect position by arching the back and swinging the legs out and down while forcing the chest upright
3. n. a person who has suddenly risen to a higher economic status but has not gained social acceptance of others in that class
4. adj. characteristic of someone who has risen economically or socially but lacks the social skills appropriate for this new position