Русско-англо-русский юридический словарь

A natural monopoly is a monopoly in an industry in which it is most efficient (involving the lowest long-run average cost) for production to be concentrated in a single firm. This market situation gives the largest supplier in an industry, often the first supplier in a market, an overwhelming cost advantage over other actual and potential competitors, so a natural monopoly situation generally leads to an actual monopoly. (Wikipedia)

A contract, lease, share, or other right is said to be “onerous” when the obligations attaching to it counter-balance or exceed the advantage to be derived from it, either absolutely or with reference to the particular possessor. Sweet. As used in the civil law and in the systems derived from it, (French, Scotch, Spanish, Mexican) the term also means based upon, supported by, or relating to a good and valuable consideration, i.e. one which imposes a burden or charge in return for the benefit conferred. (Black's Law Dictionary)

Another civil law classification relates to the advantage each party expects to receive from the agreement. A contract, such as a sale of goods, in which both parties expect to receive an advantage in exchange for the service or item they provide, is considered onerous. A contract where one party provides an advantage without receiving anything in return, such as a donation, is a gratuitous contract. (Civil Law Contracts by Christopher Meldrum)

A sham marriage or fake marriage is a marriage of convenience entered into purely for the purpose of gaining a benefit or other advantage arising from that status. (Wikipedia)