Synonyms for Diligent:

adj.

active (adjective)
hard-working.
all (adjective)
persevering.
attentive (adjective)
engrossed, regardful, vigilant, careful, attentive, absorbed, fascinated, cautious, Scrutinizing, Immersed, intent, observing, observant, responsible, rapt, Hearkening, alert, entranced, interested, mindful, Considering, enraptured, concerned, Concentrating, sharp, heedful, watchful.
fastidious (adjective)
discerning, literal, proper, priggish, accurate, perspicacious, mincing, flawless, severe, exacting, particular, fussy, methodical, precise, Qualmish, fastidious, prudish, punctilious, meticulous, scrupulous, conscientious, careful, persnickety, dainty, finicky, picky, epicurean, hypercritical, prim, demanding, critical, delicate, correct, squeamish, rigorous, choosy, discriminating.
hardworking (adjective)
industrious.
persevering, hard-working (adjective)
painstaking, persistent, tireless, unflagging, steadfast, conscientious, assiduous, pertinacious, attentive, studious, sedulous, earnest, indefatigable, constant, industrious, untiring, careful.
resolute (adjective)
faithful, true, determined, resolute, decisive, loyal, persistent, bold, unwavering, fearless, dauntless, committed, indefatigable, devoted, plucky, headstrong, reliable, resolved, strong-willed, deliberate, ruthless, dedicated, persevering, tireless, iron-willed, firm, inexorable, dogged, unchangeable, spunky, courageous, steadfast, decided, tough, intent, insistent, thorough, strong-minded, zealous, stubborn, unyielding, bullheaded, stern, serious, staunch, indomitable, unbending, constant, set, steely, unflinching, tenacious, hearty, willing, unshakeable, steady, relentless, valiant, implacable, uncompromising, earnest.
tenacious (adjective)
undaunted, unflagging, enduring, obstinate, dogged, steadfast, dauntless, hearty, stiff, flintlike, spunky, strong-willed, resolute, bullheaded, persevering, insistent, decisive, bulldogged, fervent, stubborn, determined, hard, bold, true, persistent, headstrong, devoted, faithful, tireless, obdurate, indomitable, brave, tough, plucky, indefatigable, staunch, courageous, tenacious, stony, strong.
untiring (adjective)
indefatigable.
vigilant (adjective)
sharp-eyed, mindful, watchful, particular, alert, meticulous, attentive, prepared, scrupulous, regardful, thorough, responsible, guarded, fastidious, fussy, precise, careful, prudent, finical, strict, exacting, thoughtful, conscientious, heedful, observant, ready, cautious, vigilant, provident.

n.

systematic, exact, organized. studious. diligent (noun)
industrious, tireless, sedulous, persevering, untiring, assiduous, hardworking, patient.
industrious (noun)
painstaking, unremitting, studious, purposeful, hard-working, involved, keen, pertinacious.

Other synonyms:

hard-working. industrious
industrious, studious.

Usage examples for diligent

  1. The composition of his tragedies and of the Annals, while making most demand on his original gifts, implied also a diligent study of Homer and of the Greek tragedians, and a large acquaintance with the traditions and antiquities of Rome. – The Roman Poets of the Republic by W. Y. Sellar
  2. It is enough to say as to these years, that he continued to be diligent in the acquirement of varied knowledge; that he carefully attended to his military duties; that he took active part in the volunteer movement; and in town and country was alike popular, from his love of manly sport as well as of the pursuits of art. – Speeches and Addresses of H. R. H. the Prince of Wales: 1863-1888 by Edward VII