A person who feels regret is regretful. The incident or situation that causes regret is regrettable:
The murderer said he was deeply regretful of the pain he had caused the victim's family.
I'm regretful of my decision not to study abroad. I should have traveled when
I had the chance.
The church had to be repaired after a regrettable incident of vandalism.
The two companies failed to reach an agreement due to a regrettable miscommunication. The CEO was regretful that the opportunity for a partnership was lost.
This rule - regretful for the person's feelings, and regrettable for the situation -extends to the adverb forms regretfully and regrettably.
He regretfully informed the judges that he would be withdrawing from the competition. Regrettably, he had injured his ankle in the previous round.
Regrettably, the new law increased unemployment instead of decreasing it. One senator regretfully said that voting in favor of the law had been a mistake.
Fact
Detroit policeman William L. Potts is credited with inventing the modern street traffic light in 1920. He worked out an electric light system that allowed him to control three street intersections from one tower He picked the red, yellow and green because railroads used them. .. More >>