proscenium n.

word-forming element meaning "forward, forth, toward the front" (as in proclaim, proceed); "beforehand, in advance" (prohibit, provide); "taking care of" (procure); "in place of, on behalf of" (proconsul, pronoun); from Latin pro (adv., prep.) "on behalf of, in place of, before, for, in exchange for, just as," which also was used as a first element in compounds and had a collateral form por-.

Also in some cases from cognate Greek pro "before, in front of, sooner," which also was used in Greek as a prefix (as in problem). Both the Latin and Greek words are from PIE *pro- (source also of Sanskrit pra- "before, forward, forth;" Gothic faura "before," Old English fore "before, for, on account of," fram "forward, from;" Old Irish roar "enough"), extended form of root *per- (1) "forward," hence "in front of, before, toward, near," etc.

The common modern sense of "in favor of, favoring" (pro-independence, pro-fluoridation, pro-Soviet, etc.) was not in classical Latin and is attested in English from early 19c.

1530s, "subdivision of an act of a play," also "stage-setting," from French scène (14c.), from Latin scaena, scena "scene, stage of a theater," from Greek skēnē "wooden stage for actors," also "that which is represented on stage," originally "tent or booth," which is related to skia "shadow, shade," via the notion of "something that gives shade" (see Ascians).

According to Beekes' sources, the Greek word "originally denoted any light construction of cloth hung between tree branches in order to provide shadow, under which one could shelter, sleep, celebrate festivities, etc."

A theatrical word; the wider senses come from the notion of the painted drops and hangings on stage as the "setting" for the action. From "stage setting" the sense extended to "material apparatus of a theatrical stage, part of a theater in which the acting is done" (1540s), which led to "setting of any artistic work, place in which the action of a literary work is supposed to occur" and the general (non-literary) sense of "place where anything is done or takes place" (both by 1590s).

Hence the sense in reference to a (specified) activity and its realm or sphere (1931, as in the poetry scene) and U.S. slang sense of "setting or milieu or situation for a specific group or activity," attested from 1951 in Beat jargon.

Meaning "any exhibition, display, or demonstration of strong feeling," especially "stormy encounter between two or more persons," is attested by 1761. By 1650s as "a view presented to the mind or eye." 

Behind the scenes "having knowledge of affairs not apparent to the public" (1748) is an image from the theater, "amid actors and stage machinery" (back of the visible stage and out of sight of the audience), which is attested from 1660s. Scene of the crime is attested by 1843. To make a scene "make a noisy or otherwise unpleasant demonstration" is by 1831.

The word was in Middle English in the Latin form, scena, "structure on a stage for dramatic recitations" (late 14c.).