Noun
plesiomorphy (plural plesiomorphies)
(cladistics) A character state that is present in both outgroups and in the ancestors
By contrast, for a group within the tetrapods, such as birds, having four limbs is a plesiomorphy. Source: Internet
The terms plesiomorphy and apomorphy are relative; their application depends on the position of a group within a tree. 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