from The American Heritage® Dictionary of the English Language, 5th Edition.
- noun An additional cognomen given to a Roman citizen, often in honor of military victories.
from The Century Dictionary.
- noun An additional name given by the Romans to an individual in allusion to some quality, circumstance, or achievement by which he was distinguished, as Africanus added to the name of P. Cornelius Scipio; hence, in modern use, any additional name or epithet conferred on a person.
from the GNU version of the Collaborative International Dictionary of English.
- noun An additional or fourth name given by the Romans, on account of some remarkable exploit or event.
- noun An additional name, or an epithet appended to a name.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun An
additional cognomengiven, as an honour, to a Roman citizen.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- noun an additional name or an epithet appended to a name (as in `Ferdinand the Great')
from The American Heritage® Dictionary of the English Language, 4th Edition
(link) You might have been aiming for the word agnomen, which is what Romans called nicknames.
The Roman terms agnomen and cognomen were eliminated after consultation with Hsing I-tien of
Sometimes there was also a fourth name, called the agnomen, added from some illustrious action, or remarkable event.
He was thin in person and low in stature, with light sandy-coloured hair, and small pale features, from which he derived his agnomen of BEAN or white; and although his form was light, well proportioned and active, he appeared, on the whole, rather a diminutive and insignificant figure.
Tiberius, received the agnomen of Caligula, a caligulis sine caligis levioribus, quibus adolescentior usus fuerat in exercitu Germanici patris sui.
Metellus was recalled, enjoyed a triumph, and received the agnomen of
They were twice defeated in 148 by the praetor QUINTUS CAECILIUS METELLUS, who gained the agnomen of MACEDONICUS.
To these names was sometimes added another, the _agnomen_, given for some exploit, or to show that the person was adopted from some other gens.
The second agnomen recalls the fact of his victory over the Carthaginians, while the addition of the word 'minor' distinguishes him from the former wearer of the same title.
The agnomen adoptivum indicates his transference by adoption from one gens to another.