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

Class V. Words Releasing to the Voluntary Powers
Division (II) Intersocial Volition
Section III. Conditional Intersocial Volition

772. Observance.

   NOUN:OBSERVANCE, performance, compliance, acquiescence, concurrence; obedience [See Obedience]; fulfillment or fulfilment, satisfaction, discharge; acquittance, acquittal.
  ADHESION, acknowledgment; fidelity (probity) [See Probity]; exact [See Truth]- observance; unswerving fidelity to.
   VERB:OBSERVE, comply with, respect, acknowledge, abide by; cling to, adhere to, be faithful to, act up to; meet, fulfill or fulfil; carry out, carry into execution; execute, perform, keep, satisfy, discharge; do one’s office.
  KEEP FAITH WITH; perform -, fulfill -, discharge -, acquit oneself of- an obligation; make good; make good -, keep- one’s -word, – promise; redeem one’s pledge; stand to one’s engagement.
   ADJECTIVE:OBSERVANT, faithful, true, loyal; honorable [See Probity]; true as the dial to the sun, true as the needle to the pole; punctual, punctilious, scrupulous, meticulous; literal (exact) [See Truth]; as good as one’s word.
   ADVERB:FAITHFULLY &c. adj.; to the letter.
  1. Ignoscito sæpe alteri nunquam tibi.
  2. Tempori parendum.
  3. To God, thy country, and thy friend be true.—Vaughan
  4. He that sweareth to his own hurt, and changeth not.—Bible