To underscore is to draw special attention to a fact, idea, or situation. When you're involved in a debate, it’s wise to underscore the points that best support your argument.
Literally, underscore means “to underline,” or draw a line beneath a word to emphasize it. In common speech, to underscore something is to call attention to it. If a worker sustained an injury on the job, for instance, the event would underscore the need for workplace safety. Underscore is also used to mean "emphasize." During a job interview, you want to underscore any experience that relates to the job you are applying for.