These words, derived from a Latin term meaning "destiny" or "fate," have distinct meanings. Fatal means "causing death" or "capable of resulting in destruction or ruin": "The highway accident was fatal to four persons." "Your lack of support will be fatal to my campaign." Synonyms for fatal include deadly, lethal, and mortal. Fateful means "important," "highly significant," "involving momentous consequences": "The meeting between Hitler and Mussolini was fateful for the history of Europe and the entire world." Fateful may mean "fatal," as in the preceding example, but what is fatal is not always fateful: Your unwillingness to lend me money to buy a coat may be fatal to my wardrobe plans but is hardly a fateful occurrence.
Dictionary of problem words and expressions. Harry Shaw. 1975.