WordWeb Online

1. In an unnatural way
   "his other arm lay across his chest, unnaturally, as if placed there deliberately, for a purpose"
    
2. Not according to nature; not by natural means
   "unnaturally induced conditions";
   - artificially, by artificial means
    
3. In a manner at variance with what is natural or normal
   "The early Church not unnaturally adopted the position that failure to see the messianic character of his work was really caused by the people's own blindness"

Antonym: naturally