1. One that terminates: a terminator of unpopular policies.
2. The dividing line between the bright and shaded regions of the disk of the moon or an inner planet.
3. A sequence of nucleotides that signals the end of transcription or translation and the completion of the synthesis of a nucleic acid or protein molecule.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.