diligent
adj.working hard and being very careful to do things correctly. You are diligent when you put a lot of effort into your tasks and don't rush them.
adj.characterised by steady, earnest, and energetic effort in a task or duty. Often used to describe professional or academic conduct.
“She is a diligent student who always finishes her homework early.”
“The lawyer was diligent in checking every document for errors before the trial began.”
“Through diligent research and careful cross-referencing of historical archives, the biographer uncovered several previously unknown facts about the author's early life.”
Typically used attributively before a noun or predicatively after a linking verb like 'be' or 'remain'.
From Middle English diligent, from Old French diligent, from Latin dīligēns (“careful, attentive, diligent”), present participle of dīligō (“to love, esteem much”, literally “to choose, select”), from dī-, dis- (“apart”) + legō (“to choose”); see elect and select.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.