(Mic 5:2), another name for "families" or "clans" (see Nu 1:16; 10:4; Jos 22:14,21). Several "thousands" or "families" made up a "tribe."
These are they that were called of the congregation, the princes of the tribes of their fathers; they were the heads of the thousands of Israel.
And if they blow but one, then the princes, the heads of the thousands of Israel, shall gather themselves unto thee.
and with him ten princes, one prince of a fathers house for each of the tribes of Israel; and they were every one of them head of their fathers houses among the thousands of Israel.
Then the children of Reuben and the children of Gad and the half-tribe of Manasseh answered, and spake unto the heads of the thousands of Israel,
But thou, Beth-lehem Ephrathah, which art little to be among the thousands of Judah, out of thee shall one come forth unto me that is to be ruler in Israel; whose goings forth are from of old, from everlasting.
American Standard Version Public Domain