Terminator

noun

1. One that terminates.

   "a terminator of unpopular policies."

2. The dividing line between the bright and shaded regions of the disk of a moon or planet that is illuminated by the sun.
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.
4. One who or that which terminates.
5. In astronomy, the dividing-line between the illuminated and the unilluminated part of a heavenly body.