The act or the faculty of observing or taking notice; the act of seeing, or of fixing the mind upon, anything.
The result of an act, or of acts, of observing; view; reflection; conclusion; judgment.
Hence: an expression of an opinion or judgment upon what one has observed; a remark.
Performance of what is prescribed; adherence in practice; observance.
The act of recognizing and noting some fact or occurrence in nature, as an aurora, a corona, or the structure of an animal.
Specifically, the act of measuring, with suitable instruments, some magnitude, as the time of an occultation, with a clock; the right ascension of a star, with a transit instrument and clock; the sun's altitude, or the distance of the moon from a star, with a sextant; the temperature, with a thermometer, etc.