Regrettable means unfortunate or deserving regret. When something is regrettable, it's disappointing or wrong in a way that makes you wish it hadn't happened. A regrettable decision is one you look back on and think, “I wish I'd chosen differently.”

If you say something unkind to a friend in a moment of anger, that's a regrettable comment. You didn't mean to hurt their feelings, but you did, and now you wish you could take it back. When a teacher makes a regrettable mistake while grading and has to correct it later, she feels bad about the error even though it wasn't intentional.

The word often appears in apologies or formal statements: “The confusion about the schedule was regrettable” means “We're sorry that happened and wish it hadn't.” Notice that calling something regrettable doesn't always mean someone did something terrible. Sometimes regrettable things just happen through bad luck or honest mistakes, but they still leave you wishing things had gone differently.