Natural is the opposite of unnatural.
Is this plant unnatural?
The dark, ominous clouds gave an unnatural appearance to the valley below. The sound of his voice through the microphone was unnatural. The great strength of the Incredible Hulk is unnatural.
The way to spell the word is unnatural.
A good way to use retentive in a sentence is... "How do you use the word retentive in a sentence?"
use it by saying- how can you use the word ebullient in a sentence?
His friends thought that Harry showed an unnatural interest in death.
How do you use the word gerontology in a sentence?
How can you use the word infectious in a sentence
Can you use the word concluding in a sentence? Done.
You can use the word Truss in a sentence like this.
Just use it! Or do you mean, can you use the word beheld in a sentence.
You can use an underscore to remove a word out of a sentence. It can be placed where the word was.
Since that is not a word I would not attempt to use it in a sentence.