Observance, n.
Etymology: [F.observance, L. observantia. See Observant.]
1. The act or practice of observing or noticing with attention; a heeding or keeping with care; performance; -- usually with a sense of strictness and fidelity; as, the observance of the Sabbath is general; the strict observance of duties. It is a custom More honored in the breach than the observance. Shak.
2. An act, ceremony, or rite, as of worship or respect; especially, a customary act or service of attention; a form; a practice; a rite; a custom. At dances These young folk kept their observances. Chaucer. Use all the observance of civility. Shak. Some represent to themselves the whole of religion as consisting in a few easy observances. Rogers. O I that wasted time to tend upon her, To compass her with sweet observances! Tennyson.
3. Servile attention; sycophancy. [Obs.] Salads and flesh, such as their haste could get, Served with observance. Chapman. This is not atheism, But court observance. Beau. & Fl.
Syn. -- Observance, Observation. These words are discriminated by the two distinct senses of observe. To observe means (1) to keep strictly; as, to observe a fast day, and hence, observance denotes the keeping or heeding with strictness; (2) to consider attentively, or to remark; and hence, observation denotes either the act of observing, or some remark made as the result thereof. We do not say the observation of Sunday, though the word was formerly so used. The Pharisees were curious in external observances; the astronomers are curious in celestial observations. Love rigid honesty, And strict observance of impartial laws. Roscommon.
Shades of meaning
Fernald has no entry of its own for observance; he lists it under sacrament.
Where he writes about it:
An observance has more than a formal obligation, reaching or approaching a religious sacredness; a stated religious observance, viewed as established by authority, is called an ordinance; viewed as an established custom, it is a rite. — from sacrament
The Lord's Supper is the Scriptural name for the observance commemorating the death of Christ; the word communion is once applied to it (1 Cor. x, 16), but not as a distinctive name; at an early period, however, the name communion was so applied, as denoting the communing of Christians with their Lord, or with one another. — from sacrament