How to … Correctly form a specific (or infraspecific) epithet
The name of a species is a combination of the name of a genus and a specific epithet. The name of an infraspecific taxon is a combination of the name of a species and an infraspecific epithet. The specific or infraspecific epithet can be derived from any source whatever and is either an adjective agreeing in gender with the generic name, a genitive noun, a nominative noun or a word treated as such, or two or more united or hyphenated words.
Check the following:
If the epithet is adjectival, it agrees in gender with the generic name
if the epithet honours a person, check that its gender and number match the person(s) honoured
if the epithet references a place, check that it has an appropriate place-referencing ending
if the epithet is a nominative noun, specify this in the etymology section of the protologue
Take great care when forming an epithet, ensuring in particular that it has the correct termination. Names with incorrectly-formed epithets may be validly published, but they must be corrected; this creates confusion, and is embarrassing.
An excellent resource with rules for correctly forming epithets is Botanical Latin by W. T. Stearn. Another excellent resource for finding suitable words for forming epithets is Composition of Scientific Words by R. W. Brown.
Note that a specific epithet may not exactly repeat its generic name (e.g. “Linaria linaria”); this is termed a tautonym and cannot be validly published.
While epithets are most commonly chosen to either describe a characteristic feature of the organism, reference a place where the organism is found, or honour a person, they may also be anagrams of other epithets or even nonsense words, so long as they are correctly formed.
Take care when choosing to reference a place: such epithets become inappropriate (though valid publication and legitimacy are unaffected) if the species is later found to be widely distributed rather than narrowly endemic to the place referenced.
Be aware that authors may in the future choose to sink into the synonymy of another genus the genus in which you have described a species. If this is the case and your specific epithet is preoccupied in that other genus, your epithet will need to be replaced. It is good practice to use epithets that are not already used in closely related genera.
For more information, see Chapter 5 How to publish a new name in The Code Decoded.