assiduous
/əˈsɪdjuːəs/adjective
Showing steady, careful effort; diligent and persistent in one's work.
Example sentences
- “Her assiduous preparation paid off when she passed the exam easily.”
- “An assiduous student, he reviewed his notes every evening without fail.”
Formal; the adverb "assiduously" may be met more often than the adjective. "Diligent" is the plainer choice.