WordWeb Online

1. Never-ceasing
   - relentless, unrelenting
    
2. Continually recurring to the mind
   - haunting
    
3. Retained; not shed
   "persistent leaves remain attached past maturity"; "the persistent gills of fishes"
   - lasting
    
4. Stubbornly unyielding
   - dogged, dour, pertinacious, tenacious, unyielding

See also: continual, obstinate, persist, persistence, persistency, persistently, stubborn, unforgettable, unregenerate

Antonym: caducous

Encyclopedia: Persistent