The BREAK command can be used to cut a segment from a line, polyline or arc. It is called from the Modify drop down menu as shown below.

The BREAK command

How to use BREAK  How to use the BREAK tool.

Tip: A break at (@) option is available. Issue the command BREAK, select the entity and when asked fro the second point, type @. The line is broken into two with contiguous end and start point 

How to use BREAK Breaking various entities.

Break command  Take care when using BREAK to split polylines. 

Break command