Definition of "observable" []

• Possible to observe: observable phenomena; an observable change in demeanor. See Synonyms at noticeable. (adjective)
• Deserving or worthy of note; noteworthy: an observable anniversary. (adjective)
• A physical property, such as weight or temperature, that can be observed or measured directly, as distinguished from a quantity, such as work or entropy, that must be derived from observed quantities. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Because we have to admit that we can observe only a relatively small patch of the Universe, which we call our observable Universe and we are limited by an observation horizon beyond which we will never be possible to look through."
• "The observable is conserved if and only if the equations of motion are invariant under the transformations generated by the corresponding [Hermitian] operator"
• "Nah, just an interest in observable reality … why do you dislike that so much?"