assiduous

uuttera, ahkera hard-working Hard-working, diligent or regular (in attendance or work); industrious.
1831, w:Sir Walter Scott|Sir Walter Scott, The Surgeons Daughter'', ch. 2:

He was officious in the right time and place, quiet as a lamb when his patron seemed inclined to study or to muse, active and assiduous to assist or divert him whenever it seemed to be wished.

He died after three weeks' illness, during which Mrs. Penniman, as well as his daughter, had been assiduous at his bedside.

A good deal of assiduous attention had enabled Henry to win this place in her affections.

Klein rose to prominence in the 1960s by assiduous application of accounting methods to the music industry.