It's a horizontal line that places the furthest date or event on the left end and the nearest date or event on the right end. Other important dates/events are placed as dash marks on the line in accordance to their occurence in history relative to the dates surrounding it.
Straight line
Straight line
a straight line
A curved line is a line that is curved.
A linear line is a straight line
a line across
Just a very zig-zag line through time. See example.
If the line has ends, then it's a line segment.
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a line
a line graph looks like a stocks chart