Noah Webster's New International Dictionary of the English Language

1. (n.) The act noticing with special attention; a heeding or keeping with care; as, the observance of the Sabbath is general; the strict observance of duties.

2. (n.) 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.

3. (n.) Servile attention; sycophancy.