What does nonce mean?
A nonce is a value intended to be used only once or to be unique within a particular operation. It is especially common in cryptography, where a server or client may generate a random number as part of a challenge, proof of freshness, or protection against replay attacks. A nonce is not necessarily random, but its essential property is that an attacker should not be able to reuse it to create a valid response. The word also has older literary meanings: a nonce word is a term invented for a special occasion, and a nonce form is an expression peculiar to a particular work or context. These older senses are now rare compared with the technical one. In everyday discussion, the word remains specialized, but it offers a memorable expression for a deliberately unique or one-time value.
A value, often randomly generated, that is used only once or is intended to be unique within a particular operation. The word can also denote a word or phrase coined for a special occasion.
"Each request contains a newly generated nonce that makes the authentication challenge unique."
The computing sense is now dominant; the older literary sense survives chiefly in the expressions “nonce word” and “nonce form.”
Occurring only for a particular occasion or context, especially as a newly coined word or a form peculiar to a work.
"The editor accepted the nonce expression because it suited the poem's unusual subject."
This adjective is literary and uncommon, occurring chiefly in “nonce form” and “nonce word.”
The regular plural is “nonces.” In cryptographic descriptions, “single-use nonce” and “nonce reuse” refer to whether the same value is ever applied again.
"The protocol should reject responses containing stale or repeated nonces."
A nonce is a value's one-time-use badge: valuable precisely because it should never be reused.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does nonce come from?
The word's English lineage runs through Middle English nones, meaning “once” or “for the occasion,” and ultimately Latin nones, a designation for the ninth day of the Roman month. It developed a literary sense for a word or phrase invented for a particular occasion and later acquired the now-familiar technical sense of a value intended for one-time use in computing and cryptography.
Related word forms
How nonce is actually used
In modern technical usage, “nonce” usually means a cryptographic or computational value with a non-reuse or uniqueness requirement; it need not be random if some other mechanism guarantees the required property. The older literary senses, including “nonce word” and “nonce form,” are uncommon outside discussions of style or rhetoric.