persistent

  1. continually recurring to the mind

    Synonyms : haunting
  2. never-ceasing

    Synonyms : relentless, unrelenting
  3. stubbornly unyielding

    Synonyms : dogged, dour, pertinacious, tenacious, unyielding
  4. retained; not shed

    Synonyms : lasting
    Antonyms : caducous
    Examples :
    • persistent leaves remain attached past maturity
    • the persistent gills of fishes

phenomenon

  1. any state or process known through the senses rather than by intuition or reasoning

    Type Of : process, physical process
  2. a remarkable development

    Type Of : development