38 synonyms for diligent such as attentive, active, and assiduous. Diligent is an adjective, and its antonyms are lazy and casual.
Active, assiduous, attentive, busy, careful, committed, conscientious, constant, dedicated, dogged, driven, earnest, exacting, hard-working, heedful, indefatigable, industrious, intent, laborious, meticulous, painstaking, particular, persevering, persistent, pertinacious, plodding, punctilious, rigorous, sedulous, slogging, studious, tenacious, thorough, tireless, unflagging, untiring, and zealous.