1. (

• persistent ,
• relentless ,
• unrelenting

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

2. (

• haunting ,
• persistent

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

3. (

• persistent ,
• lasting ,

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

4. (

• dogged ,
• dour ,
• persistent ,
• pertinacious ,
• tenacious ,
• unyielding

) 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" ;