Imprecation, n.
Etymology: [L. imprecatio: cf. F. imprécation.]
The act of imprecating, or unvoking evil upon any one; a player that a curse or calamnity may fall on any one; a curse. Men cowered like slaves before such horrid imprecations. Motley.
Syn. -- Malediction; curse; execration; anathema. See Malediction.
Shades of meaning
Fernald has no entry of its own for imprecation; he lists it under oath.
Where he writes about it:
Anathema, curse, execration, and imprecation are modes of invoking vengeance or retribution from a superhuman power upon the person against whom they are uttered. — from oath
Execration expresses most of personal bitterness and hatred; imprecation refers especially to the coming of the desired evil upon the person against whom it is uttered. — from oath