x_{1} and x_{2} are mutual sibling nodes in a directed tree graph x_{6} such that their shared parent node(s) x_{5} is/are the most-recent common direct ancestor of x_{3} and x_{4}, such that x_{1} is a direct ancestor of or simply is x_{3} (as the case may be), and such that x_{2} is a direct ancestor of or simply is x_{4} (as the case may be), all according to tree ordering relation x_{7}.

x_{3} and x_{4} must be distinct nodes in the same directed tree; else this relationship is undefined. If x_{3} is a direct ancestor of x_{4}, or vice-versa, then this relationship is – again – undefined. x_{6} and x_{7} define the relations/standards which are being applied. This word may be used in reference to non-familial tree graphs via analogy, despite references to 'siblings' etc. See also: "tunba", "dzena", "treicu", "tseingu", "kraune". At the time of creation, there was no commonly-recognized or succinct terminology, description, or phrase for this relationship in English to Curtis Franks' knowledge, other than something substantially similar to that which has been presented in the definition or gloss keywords.