WordWeb Online

1. Never-ceasing
   "the persistent beat of the drums";
   - relentless, unrelenting
    
2. Stubbornly persisting, refusing to give up
   - dogged, dour, pertinacious, tenacious, unyielding
    
3. Continually recurring to the mind
   "persistent memories";
   - haunting
    
4. (biology) retained; not shed
   "persistent leaves remain attached past maturity"; "the persistent gills of fishes";
   - lasting
    
5. (computing) of data or a data structure:existing after the execution of the program that creates it

See also: continual, obstinate, stubborn, unforgettable, unregenerate

Encyclopedia: Persistent, bioaccumulative and toxic substances