1.
If you describe something as unnatural, you mean that it is strange and often frightening, because it is different from what you normally expect.
The aircraft rose with unnatural speed on take-off...
The altered landscape looks unnatural and weird.
ADJ
• unnaturally
The house was unnaturally silent.
...unnaturally cold conditions.
ADV: ADV adj
2.
Behaviour that is unnatural seems artificial and not normal or genuine.
She gave him a bright, determined smile which seemed unnatural.
= false
ADJ: usu v-link ADJ
• unnaturally
Try to avoid shouting or speaking unnaturally.
ADV: ADV with v