Fateful
Part of speech: adjective
Definition: Momentous, significant, setting or sealing ones fate. Determined in advance by fate, fated.
Fatal
Part of speech: adjective
Definition: Proceeding from, or appointed by, fate or destiny.Foreboding death or great disaster.Causing death or destruction.
Example sentence: The fatal metaphor of progress, which means leaving things behind us, has utterly obscured the real idea of growth, which means leaving things inside us.