imperceptibly

/ˌɪmpərˈsɛptəbli/
adverb
  1. In a way that is impossible or extremely difficult to notice; very gradually or slightly.
    • The sun set imperceptibly, turning the sky from blue to deep purple.
    • The economy improved imperceptibly over several months.
    • He imperceptibly moved his hand closer to hers.
What does "imperceptibly" mean? | whatsthatwordmean | whatsthatwordmean