persistent

never-ceasing; "the relentless beat of the drums"

continually recurring to the mind; "haunting memories"; "the cathedral organ and the distant voices have a haunting beauty"- Claudia Cassidy

retained; not shed; "persistent leaves remain attached past maturity"; "the persistent gills of fishes"

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"