E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Demurrage.
An allowance made to the master or owners of a ship by the freighters for detaining her in port longer than the time agreed upon. (Latin, demorari, to delay.)
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The extra days beyond the lay days . are called days of demurrage.Kent: Commentaries, vol. iii. part v. lecture xlvii. p. 159.