also deaccession, "remove an entry for an item from the register of a museum, library, etc." (often a euphemism for "to sell"), by 1968, from de- "off, away" + accession, which had been used since 1887 in library publications as a verb meaning "to add to a catalogue." Related: De-accessioned; de-accessioning.
1610s, "the university building in Alexandria," from Latin museum "library, study," from Greek mouseion "place of study, library or museum, school of art or poetry," originally "a temple or shrine of the Muses," from Mousa "Muse" (see muse (n.)). The earliest use in reference to English institutions was of libraries for scholarly study (1640s); the sense of "building or part of a building set aside as a repository and display place for objects relating to art, literature, or science" is recorded by 1680s.