Meaning of preemergent

pre•e•mer•gent

Pronunciation: (prē"i-mûr'junt), [key]
— adj. Hort.
  1. of or pertaining to seedlings before they emerge or appear above ground: a preemergent weed-killer.
—n.
  1. a preemergence chemical, as a herbicide.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.