indiscernible

Adjective

• barely able to be perceived
  • the transition was almost indiscernible
    
  • an almost insensible change
    

• difficult or impossible to perceive or discern
  • an indiscernible increase in temperature
    

Related words

• Synonyms: 
  insensible , undetectable
• Antonyms: 
  discernible , discernable