Reduplication? Maybe. But isn't there a more poetical term for it?Reduplication shows up in many languages. Either the entire morpheme is doubled with no changes, e.g., English
putt-putt, kiSwahili
pigapiga 'to strike repeatedly' (<
piga 'to strike'), with changes, e.g., Japanese
hashi-bashi 'odds and ends' (<
hashi 'end; edge; tip; margin; point'), just the first part of the morpheme, or other kinds of changes, e.g., Greek leipo 'I leave', leloipa 'I left'. Then there is rhyming redpulication English
hokey-pokey, Yiddish
english shmenglish and ablaut reduplication English
criss-cross. Reduplication is used for different things, e.g., making words plural, present-past distinction, etc.
So,
pell-mell is rhyming reduplication.
[Addendum: there's also a rhetorical term,
anadiplosis ([T]he rhetorical repetition of one or several words; specifically, repetition of a word that ends one clause at the beginning of the next.
Men in great place are thrice servants: servants of the sovereign or state; servants of fame; and servants of business. Francis Bacon
Senatus haec intellegit, consul videt; hic tamen vivit. Vivit? Immo vero etiam in senatum venit. Cicero In Catilinam
(
Link.) But it's not quite the same thing.