What is "to start up"

start \start\ (st[aum]rt), v. i. [imp. & p. p. started; p. pr. & vb. n. starting.] [OE. sterten; akin to D. storten to hurl, rush, fall, G. st["u]rzen, OHG. sturzen to turn over, to fall, Sw. st["o]rta to cast down, to fall, Dan. styrte, and probably also to E. start a tail; the original sense being, perhaps, to show the tail, to tumble over suddenly.

1. To leap; to jump. [Obs.]

2. To move suddenly, as with a spring or leap, from surprise, pain, or other sudden feeling or emotion, or by a voluntary act.

   And maketh him out of his sleep to start.
   --Chaucer.

   I start as from some dreadful dream.
   --Dryden.

   Keep your soul to the work when ready to start aside.
   --I. Watts.

   But if he start, It is the flesh of a corrupted heart.
   --Shak.

3. To set out; to commence a course, as a race or journey; to begin; as, to start in business.

   At once they start, advancing in a line.
   --Dryden.

   At intervals some bird from out the brakes Starts into voice a moment, then is still.
   --Byron.

4. To become somewhat displaced or loosened; as, a rivet or a seam may start under strain or pressure.

   To start after, to set out after; to follow; to pursue.

   To start against, to act as a rival candidate against.

   To start for, to be a candidate for, as an office.

   To start up, to rise suddenly, as from a seat or couch; to come suddenly into notice or importance.