phase (v.) Look up phase at
"to synchronize," 1895, from phase (n.). Meaning "to carry out gradually" is from 1949, hence phase in "introduce gradually" (1954), phase out (1954). Related: Phased; phasing.
phase (n.) Look up phase at
1705, "phase of the moon," back-formed as a singular from Modern Latin phases, plural of phasis, from Greek phasis "appearance" (of a star), "phase" (of the moon), from stem of phainein "to show, to make appear" (from PIE root *bha- (1) "to shine"). Latin singular phasis was used in English from 1660. Non-lunar application is first attested 1841. Meaning "temporary difficult period" (especially of adolescents) is attested from 1913.