tautonym

A binomial name consisting of the same word twice, such as Bison bison.

And that would mean a species named Leucanthemum leucanthemum, with the genus and species epithet the same (a tautonym), which is a total no-no in botany.

A word or term made from two identical parts or syllables, such as bonbon or dada.

The chapter on reduplication - "flip-flopping higgledy- piggledy through the riffraff" - differentiates rhyming compounds like bigwig, hotshot, ragtag, sci-fi from repetitions called tautonyms, such as bye-bye, so-so, rah-rah, as well as from ricochet words in which the repeated element is modified: chit-chat, roly-poly, shilly-shally.

An absolute synonym.