constant in effort to accomplish something; attentive and persistent in doing anything:
a diligent student.
2.
done or pursued with persevering attention; painstaking:
a diligent search of the files.
Origin
1300-50;Middle English (< Anglo-French) < Latindīligent- (stem of dīligēns), present participle of dīligere to choose, like, equivalent to dī-di-2 + -ligere (combining form of legere to choose, read); see -ent