tenacious
te-na-cious
adjective
Holding firmly to something; very determined and persistent, not easily letting go.
"Her tenacious spirit helped her achieve success."
Thesaurus
Synonyms: recollective, retentive, long, unyielding, obstinate, dour, pertinacious, persistent, dogged, stubborn, unregenerate, coherent
Antonyms: forgetful, short, unretentive