mid-13c., "story of a building, raised floor for exhibitions," from Old French estage "a story or floor of a building, stage for performance," from Vulgar Latin *staticum "a place for standing," from Latin statum, past participle of stare "to stand" (see stet). Meaning "platform for presentation of a play" is attested from late 14c.; generalized for "profession of an actor" from 1580s.
Sense of "period of development or time in life" first recorded early 14c., probably from Middle English sense of "degree or step on the 'ladder' of virtue, 'wheel' of fortune, etc.," in parable illustrations and morality plays. Stage mother is from 1919. Stage-Door Johnny "young man who frequents stage doors seeking the company of actresses, chorus girls, etc." is attested from 1912. Stage-struck is from 1813; earlier stage-smitten (1680s). Stage whisper first attested 1865.
A period in the course of a disease.
The platform on a microscope that supports a slide for viewing.
A particular step, phase, or position in a developmental process.