Phenomenon \Phe*nom"e*non\, n.; pl. Phenomena. [L. phaenomenon, Gr. faino`menon, fr. fai`nesqai to appear, fai`nein to show. See Phantom.]

1. An appearance; anything visible; whatever, in matter or spirit, is apparent to, or is apprehended by, observation; as, the phenomena of heat, light, or electricity; phenomena of imagination or memory.

In the phenomena of the material world, and in many of the phenomena of mind. --Stewart.

2. That which strikes one as strange, unusual, or unaccountable; an extraordinary or very remarkable person, thing, or occurrence; as, a musical phenomenon.

Source: Webster's Revised Unabridged Dictionary (1913)