assiduous

as•sid•u•ous

adjective — [uh-sij-oo-uhs]

definition: constant in application or effort; working diligently at a task; showing great care and perseverance.

synonyms: diligent, meticulous, persevering, industrious, attentive

example usage:

I must now say, that, after all my searching and reading, prayer and assiduous meditation have been my only resort, and by far the most useful means of light and assistance. By these have my thoughts been freed from many an entanglement.

John Owen, explaining how he finished his seven-volume commentary on Hebrews, quoted in Piper, Contending for Our All, 107.