יַחַשׂyachas meaning in Biblical Hebrew
genealogy, family register · masculine noun (related verb: hitpael הִתְיַחֵשׂ, to be enrolled by genealogy)
A family stands in a half-empty Jerusalem while an official runs his finger down an old scroll, looking for their name. Yachas is that scroll.
וָאֶקְבְּצָה אֶת־הַחֹרִים וְאֶת־הַסְּגָנִים וְאֶת־הָעָם לְהִתְיַחֵשׂ וָאֶמְצָא סֵפֶר הַיַּחַשׂ הָעוֹלִים בָּרִאשׁוֹנָה
“I gathered the nobles, the officials and the people to be enrolled by genealogy, and I found the book of the genealogy of those who came up first. (Nehemiah 7:5)”
Picture the scroll unrolled on the table: if your name isn't in the yachas, your claim doesn't count.