indiscernible
1. [ adjective ] barely able to be perceived
Synonyms: undetectable insensible
Examples:

"the transition was almost indiscernible" "an almost insensible change"

Related terms: imperceptible
2. [ adjective ] difficult or impossible to perceive or discern
Examples:

"an indiscernible increase in temperature"

Related terms: discernible
Similar spelling:   indescribable
  indescribably
  indiscipline
  indictable
  indisposed
  indiscrete
  indissoluble
  indisputable
  indiscriminate