observance

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act or practice of observing or complying with a law, custom, command, or rule.
• noun The act or custom of keeping or celebrating a holiday or other ritual occasion.
• noun A customary rite or ceremony.
• noun The act of watching; observation.
• noun Roman Catholic Church The rule governing a religious order.

from The Century Dictionary.

• noun Attention; perception; heed; observation.
• noun Respectful regard or attention; hence, reverence; homage.
• noun The act of observing, paying attention to, or following in practice; compliance in practice with the requirements of some law, custom, rule, or injunction; due performance: as, the observance of the sabbath; observance of stipulations; observance of prescribed forms.
• noun A custom, rule, or thing to be observed, followed, or kept.
• noun A rite or ceremony; an act performed in token of worship, devotion, or respect.
• noun Synonyms Observance, Observation. These words start from two different senses of the same root — to pay regard to, and to watch. Observation is watching or notice; observance is keeping, conforming to, or complying with. Observation was formerly used in the sense of observance: as, “the observation of the Sabbath is again commanded” (caption to Ex. xxxi.); “the opinions which he [Milton] has expressed respecting … the observation of the Sabbath might, we think, have caused more just surprise” (Macaulay, Milton); but this use is now obsolescent. It is desirable that the words should be kept distinct.
• noun Form, Rite, etc. See ceremony.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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
• noun 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.
• noun obsolete Servile attention; sycophancy.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The practice of complying with a law, custom, command or rule
• noun The custom of celebrating a holiday or similar occasion
• noun Observation or the act of watching
• noun religion A rule governing a religious order, especially in the Roman Catholic church

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the act of noticing or paying attention
• noun conformity with law or custom or practice etc.
• noun a formal event performed on a special occasion
• noun the act of observing; taking a patient look