WordWeb Online

1. Not obtrusive or undesirably noticeable
   "a quiet, unnoticeable life of self-denial"
   - unobtrusive
    
2. Not noticeable; not drawing attention
   "her clothes were simple and unnoticeable"
    
3. Not drawing attention
   "an unnoticeable cigarette burn on the carpet"
   - obscure

See also: inconspicuous, insignificant, invisible, noticeability, noticeableness, obviousness, patency, undistinguished, unnoticeableness, unnoticeably

Antonym: noticeable