having momentous consequences; of decisive importance; "that fateful meeting of the U.N. when...it declared war on North Korea"- Saturday Rev; "the fatal day of the election finally arrived"
causing or marked by grief or anguish; "a grievous loss"; "a grievous cry"; "her sigh was heartbreaking"; "the heartrending words of Rabin's granddaughter"
work together on a common enterprise of project; "The soprano and the pianist did not get together very well"; "We joined forces with another research group"
cooperate as a traitor; "he collaborated with the Nazis when they occupied Paris"