Synonyms of persistent

1. persistent, relentless, unrelenting, continual (vs. sporadic): usage: never-ceasing; "the relentless beat of the drums"
2. haunting, persistent, unforgettable (vs. forgettable): usage: continually recurring to the mind; "haunting memories"; "the cathedral organ and the distant voices have a haunting beauty"- Claudia Cassidy
3. persistent (vs. caducous), lasting: usage: retained; not shed; "persistent leaves remain attached past maturity"; "the persistent gills of fishes"
4. dogged, dour, persistent, pertinacious, tenacious, unyielding, stubborn (vs. docile), obstinate, unregenerate: usage: 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"