persistent in WordNet English dictionary

1. stubbornly unyielding
   "dogged persistence"; "dour determination"; "the most vocal and pertinacious of all the critics"; "a mind not gifted to discover truth but tenacious to hold it"- T.S.Eliot; "men tenacious of opinion"
   dogged  dour  persistent  pertinacious  tenacious  unyielding 
   
2. continually recurring to the mind
   "haunting memories"; "the cathedral organ and the distant voices have a haunting beauty"- Claudia Cassidy
   haunting  persistent 
   
3. retained; not shed
   "persistent leaves remain attached past maturity"; "the persistent gills of fishes"
   persistent  lasting 
   
4. never-ceasing
   "the relentless beat of the drums"
   persistent  relentless  unrelenting