The siliqua is the modern name given to small, thin, Roman silver coins produced from 4th century and later. When the coins were in circulation, the Latin word siliqua was a unit of weight defined as one-twentyfourth of the weight of a Roman solidus (coin).

The term siliqua comes from the siliqua graeca, the seed of the carob tree, which in the Roman weight system is equivalent to 1/6 of a scruple (1/1728 of a Roman pound or about 0.19 grams).

The term has been applied in modern times to the various silver coins on the premise that the coins were valued at 1/24 of the gold solidus (which weighed 1/72nd of a Roman pound) and therefore represented a siliqua of gold in value. Since gold was worth about 14 times as much as silver in ancient Rome, such a silver coin would have a theoretical weight of 2.7 grams. There is little historical evidence to support this premise. This has not prevented the term from being applied today to silver coins issued by Constantine, which initially weighed 3.4 grams, or the later silver coin of Constantius II, which weighed about 2.2 grams and 18mm, and is sometimes called a "light" or "reduced" siliqua to differentiate it. The term is one of convenience as no name for these coins is indicated by contemporary sources. Thin silver coins to the 7th century which weigh about 2 to 3 grams are known as siliqua by numismatic convention.