untiring

Synonyms: constant continued continuing dedicated devoted dogged eager beaver fireball firm go-go grind hyper incessant indefatigable indomitable inexhaustible jumping patient perky persistent pertinacious plodding plugging resolute staunch steady strong tenacious tireless unceasing undeterred unfailing unfaltering unflagging unflinching unremitting unstinted unswerving unwavering unwearied

Antonyms: failing irresolute tiring unpersevering