1. contrary to the normal course of nature; not occurring naturally
2. strange or abnormal in a way that is disturbing
3. forced or affected; not genuine or spontaneous

Examples

• The bright green color of the drink looked unnatural.
• There was an unnatural silence in the forest that made us nervous.
• His smile seemed unnatural and forced during the interview.
• The scientist created an unnatural compound in the laboratory.
• The unnatural position of the furniture made the room feel awkward.
• Her laugh sounded unnatural, as if she was trying too hard to be cheerful.