Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.

Class VI. Words Relating to the Sentient and Moral Powers
Section III. Sympathetic Affections
4. Retrospective Sympathetic Affections

917. Ingratitude.

   NOUN:INGRATITUDE, thanklessness, oblivion of benefits, unthankfulness.
  “benefits forgot” [As You Like It]; thankless task, thankless office.
   VERB:BE UNGRATEFUL &c. adj.; feel no obligation, owe one no thanks, forget benefits; look a gift horse in the mouth.
   ADJECTIVE:UNGRATEFUL, unmindful, unthankful; thankless, ingrate, wanting in gratitude, insensible of benefits.
  forgotten; unacknowledged, unthanked, unrequited, unrewarded; ill-requited; ill-rewarded.
   INTERJECTION:thank you for nothing! “et tu Brute!” [Julius Cæsar].    QUOTATIONS:
  1. Ingratitude! thou marble-hearted fiend.—Lear
  2. This was the most unkindest cut of all.—Julius Cæsar
  3. Hearts unkind, kind deeds With coldness still returning.—Wordsworth