phenomenon

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

• noun An occurrence, circumstance, or fact that is perceptible by the senses.
• noun An unusual, significant, or unaccountable fact or occurrence; a marvel.
• noun A remarkable or outstanding person; a paragon. synonym: wonder.
• noun Philosophy In the philosophy of Kant, an object as it is perceived by the senses, as opposed to a noumenon.
• noun Physics An observable event.

from The Century Dictionary.

• noun An obsolete form of phenomenon.
• noun Any physiological or pathological change apparent to the senses.
• noun Diminution of the Achilles tendon reflex in sciatica.
• noun In philosophy, an appearance or immediate object of experience, as distinguished from a thing in itself.
• noun In science, a fact directly observed, being either
• noun an individual circumstance or occurrence, such as the emergence of a temporary star, or more usually
• noun a regular kind of fact observed on certain kinds of occasion, such as the electrical sparks seen in combing the hair of some persons in cold, dry weather.
• noun Ay extraordinary occurrence or fact in nature; something strange and uncommon; a prodigy; a very remarkable personage or performer.

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

• noun See phenomenon.
• noun An appearance; anything visible; whatever, in matter or spirit, is apparent to, or is apprehended by, observation
• noun That which strikes one as strange, unusual, or unaccountable; an extraordinary or very remarkable person, thing, or occurrence.

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

• noun An observable fact or occurrence or a kind of observable fact or occurrence.
• noun Appearance; a perceptible aspect of something that is mutable.
• noun A fact or event considered very unusual, curious, or astonishing by those who witness it.
• noun A wonderful or very remarkable person or thing.
• noun philosophy An experienced object whose constitution reflects the order and conceptual structure imposed upon it by the human mind (especially by the powers of perception and understanding).

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

• noun a remarkable development
• noun any state or process known through the senses rather than by intuition or reasoning