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

Class VI. Words Relating to the Sentient and Moral Powers
Section IV. Moral Affections
1. Moral Obligations

926. Duty.

   NOUN:DUTY, what ought to be done, moral obligation, accountableness, liability, onus, responsibility; bounden -, imperative- duty; call, – of duty; accountability.
  allegiance, fealty, tie; engagement (promise) [See Promise]; part; function, calling (business) [See Business].
  OBSERVANCE, fulfillment, discharge, performance, acquittal, satisfaction, redemption; good behavior.
  MORALITY, morals, decalogue; case of conscience; conscientiousness (probity) [See Probity]; conscience, inward monitor, still small voice within, sense of duty, tender conscience; the hell within [Paradise Lost].
  PROPRIETY, fitness; dueness [See Dueness]; seemliness, amenableness, amenability, decorum, to prepon [Gr. τ&omictono; πρ&epsitono;πον]; the thing, the proper thing; the -right, – proper- thing to do.
  [SCIENCE OF MORALS] ethics, ethology [obs. in this sense]; deontology, aretology [obs.]; moral -, ethical- philosophy; casuistry, polity.
   VERB:BE THE DUTY OF, be incumbent on &c. adj.; be responsible &c. adj.; behoove, become, befit, beseem; belong to, pertain to; fall to one’s lot; devolve on; lie upon, lie on one’s head, lie at one’s door; rest with, rest on the shoulders of.
  take upon oneself (promise) [See Promise]; be -, become- -bound to, – sponsor for; incur a responsibility &c. n.; be -, stand -, lie- under an obligation; stand responsible for; have to answer for; owe it to oneself.
  enter upon -, perform -, observe -, fulfill -, discharge -, adhere to -, acquit oneself of -, satisfy- -a duty, – an obligation; act one’s part, redeem one’s pledge, do justice to, be at one’s post; do duty; do one’s duty &c. (be virtuous) [See Virtue].
  be on one’s good behavior, mind one’s P’s and Q’s; walk the straight path.
  IMPOSE A DUTY &c. n.; enjoin, require, exact; bind, – over; saddle with, prescribe, assign, call upon, look to, oblige.
   ADJECTIVE:OBLIGATORY, binding; imperative, peremptory; stringent (severe) [See Severity]; behooving &c. v.; incumbent on, chargeable on; under obligation; obliged by, bound by, tied by; saddled with.
  due to, beholden to, bound to, indebted to; tied down; compromised (promised) [See Promise]; in duty bound.
  AMENABLE, liable, accountable, responsible, answerable.
  RIGHT, meet (due) [See Dueness]; moral, ethical, casuistical, conscientious, ethological.
   ADVERB:with a safe conscience, as in duty bound, on good behavior, on one’s own responsibility, at one’s own risk, suo periculo [L.]; in foro conscientiæ [L.]; quamdiu se bene gesserit [L.]; at one’s post.
  1. Dura lex sed lex.
  2. Dulce et decorum est pro patria mori.
  3. Honos habet onus.
  4. Leve fit quod bene fertur onus.—Ovid
  5. Loyauté m’oblige.
  6. Simple duty hath no place for fear.—Whittier
  7. Stern daughter of the voice of God.—Wordsworth
  8. There is a higher law than the Constitution.—Wm. Seward
  9. So nigh is grandeur to our dust, So near is God to man, When Duty whispers low, Thou must, The youth replies, I can!—Emerson
  10. Labor to keep alive in your breast that little spark of celestial fire—conscience.—George Washington
  11. Thus conscience does make cowards of us all.—Hamlet
  12. And voices that we thought were fled Arise and call us, and we come.—Noyes