o·pus / ˈōpəs/ • n. (pl. o·pus·es or o·pe·ra / ˈäp(ə)rə/ ) 1. Mus. a separate composition or set of compositions by a particular composer, usually ordered by date of publication: The Gambler was Prokofiev's sixth opera, despite its early opus number. See also Op.2. any artistic work, esp. one on a large scale: he was writing an opus on Mexico.

opus Latin, = ‘work’.
opus Alexandrinum a pavement mosaic work widely used in Byzantium in the 9th century and later in Italy, consisting of coloured stone, glass, and semiprecious stones arranged in intricate geometric patterns.
opus anglicanum the fine pictorial embroidery produced in England in the Middle Ages, especially between c.1100 and c.1350, characterized by the depiction of lively human and animal figures, and the use of gold cloth, and used especially for ecclesiastical vestments.
opus Dei in the Christian Church, liturgical worship regarded as man's primary duty to God. The Latin phrase, meaning literally ‘the work of God’, is attributed to St Benedict but is attested from the 5th century in the sense of Divine Office or worship.

opus (Lat.). Work. Word used, followed by a number, e.g. Opus 50, for the numbering of a composer's works. This numbering gives a rough idea of the order in which works were comp., but can be misleading. Sometimes the Opus no. is allotted by the composer, sometimes by the publisher. Some composers, e.g. Mozart, Haydn, did not number their works; some, e.g. Elgar, gave some works opus nos. and not others; some, e.g. R. Strauss, did likewise but also reallotted opus nos. so that much confusion arises in his case. Dvor̆ák allowed early works to be given late opus nos. by his publisher. In many cases an opus no. covers a group of works, in which case the numbering is subdivided, e.g. Op.59, No.3, or in a style often used, Op.59/3. In other cases, 2 versions of the same work exist and the composer uses letters after the number to differentiate them, e.g. Op.49a, Op.49b. Although the Latin plural of opus is opera, it has become customary to write ‘opuses’, to avoid confusion, just as in Italian ‘opera’ has become a singular noun with the plural opere.

opus work, esp. musical composition. XVIII (first in magnum o., o. magnum great work). — L., rel. to Skr. ápa-.
So opuscule XVII. — (O)F. — L. opusculum XVII.

opus. Latin for ‘work’, as intended to designate construction, or arrangement of materials in construction.