Q: The terminal combination “-bt” is an odd one, with its silent “b,” and curiously (ignoring variations) the only two English words in which it occurs begin with “d.” Care to explicate?
A: The consonant cluster “bt” doesn’t appear only in words beginning with “d,” and it isn’t always at the end. It’s found in “doubt,” “debt,” “subtle,” and their various forms (“doubtful,” “indebted,” “subtlety,” and so on).
The “b” is now silent in these words, though it was neither seen nor heard when “doubt,” “debt,” and “subtle” first appeared in Middle English, the language used from around 1150 to 1450.
Writers began adding the “b” in the early Modern English of the late 15th and 16th centuries to make the terms look more like their Classical Latin ancestors: dubitare, debitum, and subtilis. (The “b” was pronounced in Latin, but silent in the English borrowings.)
As the classicist J. D. Sadler explains, “There are many words borrowed from Latin through French where we have gone back to the Latin root to replace a letter lost in transit. Most involve the initial consonant in the groups bt, ct, lt, and pt.”
In his article “Popular Etymology” (The Classical Journal, February-March 1971), Sadler gives “debt,” “doubt,” and “subtle” as examples, along with “arctic,” “perfect,” “subject,” “verdict,” “victuals,” “assault,” “fault,” “somersault,” and “receipt.”
In some of these words, he notes, the initial letter of the consonant cluster is mute while in others “we have recovered the sound.” He adds that “perhaps words of this sort [those Latinized retroactively] should be termed examples of scholarly etymology, rather than of popular etymology.”
(We wrote in 2018 about another consonant cluster with a silent “b”—the “mb” in words like “bomb,” “tomb,” “lamb,” “dumb,” “comb,” “climb,” and “plumb.”)
When “doubt” first appeared in early Middle English, it was a verb (duten) meaning “to dread, fear, or be afraid of,” a usage that’s now obsolete, according to the Oxford English Dictionary.
The dictionary’s first citation is from Ancrene Riwle, an anonymous guide for monastic women, written sometime before 1200. The verb here appears as duteð (duteth): “Þe deouel of helle duteð ham swiðe” (“the devil of hell dreads them [prayers] greatly”).
The earliest OED example showing the verb in its uncertain sense is from a homily written around 1325:
“Of his birth douted thai noht” (“Of his birth doubted they nought”). English Metrical Homilies From Manuscripts of the Fourteenth Century (1862), edited by John Small.
As for the noun “doubt,” Oxford says that when it appeared in the early 13th century it referred to “the (subjective) state of uncertainty with regard to the truth or reality of anything” or “undecidedness of belief or opinion.”
The dictionary’s earliest citation is from The Legend of St. Katherine of Alexandria, an anonymous work written sometime before 1225: “Ne beo þu na þing o dute / Of al þet tu ibeden hauest” (“Do not be thou the least in doubt of all that thou hast prayed for”).
When the noun “debt” showed up in the late 14th century as the plural dettis, the OED says, it meant “that which is owed or due; anything (as money, goods, or service) which one person is under obligation to pay or render to another.”
The dictionary’s earliest example is from a treatise by the theologian John Wycliffe: “Ȝif a trewe man teche þis pore man to paie his dettis” (“If a true man teach this poor man to pay his debts”). From The Grete Sentence of Curs Expounded (circa 1380).
As for “subtle,” it first appeared as an adjective describing someone “characterized by wisdom or perceptiveness; discriminating, discerning; shrewd,” according to the dictionary.
The first OED citation (with “subtle” spelled “sotil”) is from a Middle English poem about the childhood of Jesus. Here’s an expanded version of the citation:
“For leowi wuste þat Jesum / Sotil was and wis of redes” (“For loving was Jesus, subtle and wise of counsel”). From “Childhood Jesus” (c. 1300), published in 1875 as “Kindheit Jesu” in Altenglische Legenden (Old English Legendary), edited by Carl Horstmann.
And here are the earliest OED examples for “doubt,” “debt,” and “subtle” in their usual senses and spelled with a “b”:
- “Diuerse of his houshold seruauntes, whome either he [Richard III] suspected or doubted, were by great crueltie put to shamefull death.” The Vnion of the Two Noble and Illustrate Famelies of Lancastre [and] Yorke (1548), by Edward Hall. We’ve expanded the citation.
- “To declare his debtes, what he oweth.” The Booke of the Common Prayer (1549), the original Anglican prayer book, published in the reign of King Edward VI.
- “The subtle difference of lying and telling of a lye.” From an undated letter by Edward Seymour, Duke of Somerset and Lord Protector of England, in answer to a May 21, 1547, letter by Stephen Gardiner, Bishop of Winchester.
Finally, we should note that the “b” spelling of the noun “doubt” appeared somewhat earlier in its obsolete sense of fear:
“For doubte to be blamed he spored his horse” (“For fear of being blamed, he spurred his horse”). The Foure Sonnes of Aymon (1490), William Caxton’s translation of Les Quatre Fils Aymon, an anonymous French romance dating from the late 12th century.