The Collaborative International Dictionary of English v.0.48:

Phase \Phase\ (f[=a]z), n.; pl. Phases (f[=a]z"[e^]z). [NL.
   phasis, Gr. fa`sis, fr. fai`nein to make to appear: cf. F.
   phase. See Phenomenon, Phantom, and Emphasis.]
   1. That which is exhibited to the eye; the appearance which
      anything manifests, especially any one among different and
      varying appearances of the same object.
      [1913 Webster]

   2. Any appearance or aspect of an object of mental
      apprehension or view; as, the problem has many phases.
      [1913 Webster]

   3. (Astron.) A particular appearance or state in a regularly
      recurring cycle of changes with respect to quantity of
      illumination or form of enlightened disk; as, the phases
      of the moon or planets. See Illust. under Moon.
      [1913 Webster]

   4. (Physics) Any one point or portion in a recurring series
      of changes, as in the changes of motion of one of the
      particles constituting a wave or vibration; one portion of
      a series of such changes, in distinction from a contrasted
      portion, as the portion on one side of a position of
      equilibrium, in contrast with that on the opposite side.
      [1913 Webster]

   5. (Phys. Chem.) A homogenous, physically distinct portion of
      matter in a system not homogeneous; as, the three phases,
      ice, water, and aqueous vapor; in a mixture of gasoline
      and water, the gasoline will settle as the upper phase. A
      phase may be either a single chemical substance or a
      mixture, as of gases.
      [Webster 1913 Suppl.]

   6. (Zool.) In certain birds and mammals, one of two or more
      color variations characteristic of the species, but
      independent of the ordinary seasonal and sexual
      differences, and often also of age. Some of the herons
      which appear in white and colored phases, and certain
      squirrels which are sometimes uniformly blackish instead
      of the usual coloration, furnish examples. Color phases
      occur also in other animals, notably in butterflies.
      [Webster 1913 Suppl.]

   7. (Physics) the relation at any instant of any cyclically
      varying physical quantity, such as voltage in an A.C.
      circuit, an electromagnetic wave, a sound wave, or a
      rotating object, to its initial value as expressed as a
      fractional part of the complete cycle. It is usually
      expressed in angular measure, the complete cycle being
      360[deg]. Such periodic variations are generally well
      represented by sine curves; and phase relations are shown
      by the relative positions of the crests and hollows of
      such curves. Magnitudes which have the same phase are said
      to be in phase.

   Note: The concept of phase is also applied generally to any
         periodically varying phenomenon, as the cycle of
         daylight. One person who sleeps during the day and
         another who sleeps at night may be said to be out of
         phase with each other.
         [PJC]

   8. Specifically: (Elec.) The relation at any instant of a
      periodically varying electric magnitude, as electro-motive
      force, a current, etc., to its initial value as expressed
      in factorial parts of the complete cycle. It is usually
      expressed in angular measure, the cycle being four right
      angles, or 360[deg].
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Phasis \Pha"sis\, n.; pl. Phases. [NL.]
   See Phase. --Creech.
   [1913 Webster] Phasm