Read this excerpt from Franklin Delano Roosevelt's 'Pearl Harbor Address to
the Nation":
Hostilities exist. There is no blinking at the fact that our
people, our territory, and our interests are in grave danger. .
. I ask that the Congress declare that since the
unprovoked and dastardly attack by Japan on Sunday,
December 7th, 1941, a state of war has existed between
the United States and the Japanese empire.
Based on this excerpt, what is most likely the meaning of "dastardly?