solidus

Etymology

It is inherited from Middle English solidus, also solidy,^[2][3] borrowed from Late Latin solidus (“an imperial Roman gold coin”),^[3][4][5][6] in full solidus nummus (“solid coin”),^[3][4][7] properly a coin of thick or solid metal rather than thin plate.^[4] This is a noun use of the adjective solidus (“firm, whole, undivided”),^[8][9][4] the source of solid,^[10][5] from a suffixed form of Proto-Indo-European *sol- (“whole”).^[4][10] The sense "shilling" is from Medieval Latin,^[6][11] and the sloping line is a further use of the shilling word.^[6][11] Its name in phase diagrams is a separate adoption of the Latin adjective, first in German, by H. W. B. Roozeboom in 1899.^[8][6]

Earliest recorded meaning

A gold coin of the Roman Empire: before 1387, in Trevisa's translation of Higden's Polychronicon, where Barnhart reads solidy and takes it for both the English shilling and the Roman coin.^[8][3][12] The Middle English Dictionary also has the abbreviation sol. in the Peterborough Chronicle, about 1160.^[2]

Semantic evolution

Constantine introduced the coin, worth about 25 denarii, as successor to the aureus, and it lasted until the fall of the Byzantine Empire in the 15th century.^[4][6] Medieval Latin used the same word for the shilling,^[6][11] in the abbreviation £. s. d., for librae, solidi, denarii,^[7] and English used it so until 1706.^[8] The line came from writing shillings: it is explained as a lengthened long s,^[11][7] and Etymonline reports this only as something said of the sign.^[4] The dictionaries record it in 1891, as a line separating shillings from pence, as in 12/6.^[8][12][4] It is also used in writing fractions and for other separations of figures and letters.^[8][9][4] The term in physical chemistry, for the limit below which a mixture is entirely solid, dates from 1901 in English.^[8]

Timeline

• c. 1160 – the abbreviation sol., for a shilling, in the Peterborough Chronicle.^[2]
• before 1387 – a gold coin of the Roman Empire, as solidy in Trevisa.^[8][3]
• before 1398 – the form solidus.^[3]
• c. 1475 – a shilling (obsolete by 1706).^[8]
• 1891 – a sloping line between shillings and pence and in fractions, in the Century Dictionary.^[8][12][4]
• 1901 – a line or temperature in a phase diagram, below which a mixture is entirely solid.^[8]

Meanings

Noun

1. A gold coin of the later Roman and Byzantine empires, introduced by Constantine; plural solidi.^[6][11][8]
2. A sloping line (/) used in fractions and ratios and between alternatives, and formerly between shillings and pence; a slash or virgule.^[11][8][9]
3. (physical chemistry) A curve or surface in a phase diagram, or the temperature it marks, below which a mixture is entirely solid.^[6][8][9]
4. (obsolete, 1475–1706) A shilling.^[8][2]

Related words

• solid
• solder
• soldier
• sou
• safe
• solemn

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d Kurath, Hans; Kuhn, Sherman M.; Lewis, Robert E., eds. (1952–2001), Middle English Dictionary, Ann Arbor: University of Michigan Press; online edition ed. Frances McSparran et al. (2000–2018)
3. ^ a b c d e f Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
4. ^ a b c d e f g h i j Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
5. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
6. ^ a b c d e f g h Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
7. ^ a b c The Chambers Dictionary (2014), 13th ed., Edinburgh: Chambers
8. ^ a b c d e f g h i j k l m n o Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
9. ^ a b c d Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
10. ^ a b Ayto, John (2005), Word Origins: The Secret Histories of English Words from A to Z, 2nd ed., London: A & C Black
11. ^ a b c d e f Collins English Dictionary (2023), Glasgow: HarperCollins
12. ^ a b c Barnhart, Robert K., ed. (1995), The Barnhart Concise Dictionary of Etymology, New York: HarperCollins