Officer patrolling highways (7)

I believe the answer is:

trooper

(Other definitions for trooper that I've seen before include "Private soldier" , "ship" , "Cavalry soldier" , "Cavalry 21" , "Proverbially swearing soldier" .)

I've seen this clue in the Newsday.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.