Here is an example sentence with the word 'omen':
An eclipse is often seen as a bad omen back in the ancient times.
the convocation meeting was today
Monsters inc is a wonderful movie.
You're opinion on that subject is kind of heresy.
The nuclear bomb produced deadly radiation.
"Spare" and "The"
There have been at least five Omen films. The Omen(1976), Damien: Omen II (1978), Omen III: The Final Conflict (1981), Omen IV: The Awakening (1991) (TV) and The Omen (2006), which is a remake of the first movie.
Omen
personification
He should HAVE known better.
It depends on context. "The meteors were an omen of pending disaster" or "the patrol's appearance was an omen of more to come" are both acceptable.
Ominous: [Latin, ominosus < Omen] Of or being an omen, esp. an evil one. So, yes, ominous is the adjective form of omen.
Here: You made a mistake spelling the word "sentence."