1. Not observed
   - unseen 
2. Not observed
   "managed to slip away unobserved"

See also: undetected, unnoticed

• obesity diet
• obey
• obfuscate
• obfuscation
• obfuscatory
• obi
• obidoxime chloride
• obiism
• obit
• obiter
• obiter dictum
• obituary
• object
• object ball
• object code
• object glass
• object language
• object lens
• object lesson
• object of a preposition
• object of the verb
• object program
• object recognition
• object-oriented database
• object-oriented database management system