Upstart, v. i.
To start or spring up suddenly. Spenser. Tennyson.
2 other Webster entries under this spelling
Upstart, n.
1. One who has risen suddenly, as from low life to wealth, power, or honor; a parvenu. Bacon.
2. (Bot.)
The meadow saffron. Dr. Prior.
Upstart, a.
Suddenly raised to prominence or consequence. "A race of upstart creatures." Milton.
Shades of meaning
Fernald has no entry of its own for upstart; he lists it under new.
He lists it without comment; the entries above explain its neighbors.