[ feyz-in ]
/ ˈfeɪzˌɪn /


an act or instance of phasing in; gradual introduction or implementation.

Nearby words

  1. phase space,
  2. phase speed,
  3. phase transition,
  4. phase velocity,
  5. phase-contrast microscope,
  6. phase-switching,
  7. phased array,
  8. phasedown,
  9. phaseout,
  10. phases of matter

Origin of phase-in

noun use of verb phrase phase in


[ feyz ]
/ feɪz /


verb (used with object), phased, phas·ing.

to schedule or order so as to be available when or as needed.
to put in phase; synchronize: to phase one mechanism with another.

Verb Phrases

Origin of phase

1805–15; (noun) back formation from phases, plural of phasis

Related forms
Can be confusedfaze phase Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for phase in

phase in


(tr, adverb) to introduce in a gradual or cautious mannerthe legislation will be phased in over two years


/ (feɪz) /


verb (tr)

Derived Formsphaseless, adjectivephasic or phaseal, adjective

Word Origin for phase

C19: from New Latin phases, pl of phasis, from Greek: aspect; related to Greek phainein to show

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for phase in
Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for phase in


[ fāz ]


A characteristic form, appearance, or stage of development that occurs in a cycle or that distinguishes some individuals of a group.
A discrete homogeneous part of a material system that is mechanically separable from the rest, as is ice from water.
Any of the forms or states, solid, liquid, gas, or plasma, in which matter can exist, depending on temperature and pressure.
A particular stage in a periodic process or phenomenon such as a wave form or time pattern.


To introduce, one stage at a time.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for phase in


[ fāz ]

Any of the forms, recurring in cycles, in which the Moon or a planet appears in the sky.
One of a set of possible homogenous, discrete states of a physical system. States of matter such as solid and liquid are examples of phases, as are different crystal lattice structures in metals such as iron. See also phase transition state of matter.
A measure of how far some cyclic behavior, such as wave motion, has proceeded through its cycle, measured in degrees or radians. At the beginning of the phase, its value is zero; at one quarter of its cycle, its phase is 90 degrees (π/2 radians); halfway through the cycle its value is 180 degrees (π radians), and so on.♦ The phase angle between two waves is a measure of their difference in phase. Two waves of the same frequency that are perfectly in phase have phase angle zero; if one wave is ahead of the other by a quarter cycle, its phase angle 90 degrees (π/2 radians); waves that are perfectly out of phase have phase angle 180 degrees (π radians), and so on. See more at wave.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Idioms and Phrases with phase in

phase in

Introduce one stage at a time. For example, New technology must be phased in or the office will be overwhelmed. The antonym is phase out, meaning “to bring or come to an end, one stage at a time,” as in The department is phasing out all the older computers. [Mid-1900s]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.