noun
terminator
TER-muh-nay-ter/tˈɝmʌnˌeɪtɝ/
Something that brings about or marks an end.
Earth's terminator marks the curved boundary between daylight and darkness.

Etymology
The pieces express someone who sets an end or boundary. This accounts for both a boundary such as the line between planetary light and darkness and, more generally, a person or thing that ends something.
In context
when you see that line between day and night you're seeing the terminator
More examples
- The program treats a blank line as a record terminator.
- The cable needs a terminator at its far end.
- This DNA sequence functions as a terminator, stopping transcription.
Forms
terminator · terminators
terminate verb — To bring something to an end.
termination noun — The act of ending or stopping something.
Similar words
- delimiter
- A delimiter separates units; a terminator specifically ends one.
- stopper
- A stopper blocks or halts something rather than marking its end.