perseverant (adj.)

"to persist in what one has undertaken, to pursue steadily a design or course," late 14c., perseveren, from Old French perseverer "continue, persevere, endure" and directly from Latin perseverare "continue steadfastly, persist," from persevereus "very strict, earnest," from per "very" (see per) + severus "serious, grave, strict, austere," which is probably from PIE root *segh- "to have, hold," on the notion of "steadfastness, toughness." Related: Persevered; persevering.