Antonyms of adj untiring

1 sense of untiring

Sense 1
hardworking, industrious, tireless, untiring -- (characterized by hard work and perseverance)

INDIRECT (VIA diligent) -> negligent -- (characterized by neglect and undue lack of concern; "negligent parents"; "negligent of detail"; "negligent in his correspondence")

Similarity of adj untiring

1 sense of untiring

Sense 1
hardworking, industrious, tireless, untiring -- (characterized by hard work and perseverance)
       => diligent (vs. negligent) -- (characterized by care and perseverance in carrying out tasks; "a diligent detective investigates all clues"; "a diligent search of the files")