What does "prophecy" mean?

1. (a prediction) a prediction about the future, especially one that people believe comes from a god. 2. (the power of predicting) the ability or act of telling what will happen in the future.

Is it correct to say "The ancient king heard a dark prophesy."?

No — say "The ancient king heard a dark prophecy.". In modern English, 'prophecy' is the noun (the thing) and 'prophesy' is the verb (the action).

prophecy

US //ˈpɹɑfəsi// UK //pɹˈɒfəsi// prophe·cy

1 a prediction (n.)
B2 Upper Intermediate Religion

a prediction about the future, especially one that people believe comes from a god.

a prediction of future events, typically one made by a prophet or under divine inspiration.

Example

The old woman made a prophecy that the kingdom would one day fall.

Example

The oracle delivered a cryptic prophecy that the king misinterpreted, leading his army into a disastrous and unnecessary conflict.
- prediction
- forecast
- prognostication
Pitfall

The ancient king heard a dark prophesy.

The ancient king heard a dark prophecy.

In modern English, 'prophecy' is the noun (the thing) and 'prophesy' is the verb (the action).
2 the power of predicting (n.)
C1 Advanced Literary Religion

the ability or act of telling what will happen in the future.

the faculty, function, or practice of a prophet; the act of divining the future.

Example

He was believed to have the gift of prophecy from a young age.

Example

The monk was revered for his gift of prophecy, though he rarely spoke of the visions that haunted his sleep.
- divination
- revelation

Origin

From Middle English prophecie, from Old French prophetie, from Latin prophētīa, from Ancient Greek προφητεία (prophēteía, “prophecy”), from προφήτης (prophḗtēs, “speaker of a god”), from πρό (pró, “before”) + φημί (phēmí, “I tell”). Displaced native Old English wītgung. Doublet of prophesy.