The Collaborative International Dictionary
Polytomy
Polytomy \Po*lyt"o*my\, n. (Logic)
A division into many members.
--F. Bowen.
Wiktionary
polytomy
n. (context taxonomy English) A section of a phylogeny in which the evolutionary relationships can not be fully resolved to dichotomy
Wikipedia
Polytomy
In biology, a polytomy is a section of a phylogeny in which the relationships cannot be fully resolved to dichotomies, thus giving many temporally based branches. They present an analytical problem, but can usually be better studied by utilizing more flexible phylogenetic network software such as SplitsTree, which can represent some polytomies as median networks.