Synonyms of hard-working

2 Syllables
earnest, fussy, picky, punctual, studious, stickler, exact, strenuous, heedful
3 Syllables
finicky, industrious, tireless, fussbudget, conscientious, thoroughgoing, diligent, punctilious, painstaking, weariless, assiduous, careful, scrupulous, sedulous, unwearied, exacting
4 Syllables
persnickety, particular, persevering, conscionable