persistent
per-sis-tent
adjective
Continuing to exist or happen for a long time; difficult to stop.
"He had a persistent cough for weeks."
adjective
Continuing to do something despite difficulties or opposition.
"Her persistent efforts finally paid off."
Thesaurus
Synonyms: lasting, unyielding, obstinate, dour, pertinacious, dogged, tenacious, stubborn, unregenerate, unforgettable, haunting, continual