Prefix
A prefix meaning with, along with, together, at the same time. Syn- becomes sym- before p, b, and m, and syl- before l.
Source: Webster's dictionaryAutapomorphies express nothing about relationships among groups; clades are identified (or defined) by synapomorphies (from syn-, "together"). Source: Internet
When two or more taxa that are not nested within each other share a plesiomorphy, it is a symplesiomorphy (from syn-, "together"). Source: Internet