The Collaborative International Dictionary of English v.0.48:

Upstart \Up*start"\, v. i.
   To start or spring up suddenly. --Spenser. Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Upstart \Up"start`\, n.
   1. One who has risen suddenly, as from low life to wealth,
      power, or honor; a parvenu. --Bacon.
      [1913 Webster]

   2. (Bot.) The meadow saffron. --Dr. Prior.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Upstart \Up"start`\, a.
   Suddenly raised to prominence or consequence. "A race of
   upstart creatures." --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

upstart
    adj 1: characteristic of someone who has risen economically or
           socially but lacks the social skills appropriate for this
           new position [syn: nouveau-riche, parvenu,
           parvenue, upstart(a)]
    n 1: an arrogant or presumptuous person
    2: a person who has suddenly risen to a higher economic status
       but has not gained social acceptance of others in that class
       [syn: upstart, parvenu, nouveau-riche, arriviste]
    3: 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 [syn: kip, upstart]