רכס RKS, Ex. 39:21

[Isaac Fried]

We read there
וַיִּרְכְּסוּ אֶת הַחֹשֶׁן מִטַּבְּעֹתָיו אֶל טַבְּעֹת הָאֵפֹד בִּפְתִיל תְּכֵלֶת
KJV: "And they did bind the breastplate by his rings unto the rings of the ephod with a lace of blue"
In which וַיִּרְכְּסוּ = בא-היא-רכס-הוּא WA-YI-RKS-U, is from the root RKS, 'assemble, gather, fit together, congregate, cluster, collect, group'. The root is a member of the family of roots
רגז, רגש
רהט
רחץ, רחש
רכז, רכס, רכש
רקד
There are two nouns derived from this root: רֶכֶס REKES, 'hill, mound, pile, heap', as in Isaiah 40:4
כָּל-גֶּיא יִנָּשֵׂא וְכָל הַר וְגִבְעָה יִשְׁפָּלוּ וְהָיָה הֶעָקֹב לְמִישׁוֹר וְהָרְכָסִים לְבִקְעָה
KJV: "Every valley shall be exalted, and every mountain and hill shall be made low: and the crooked shall be made straight, and the rough places plain".
and ROKES (related to רוֹחֵש ROXE$, 'swarm, mob', ad also to רוֹגֵז ROGEZ), as in Ps. 31:20-21.

In spoken Hebrew רוכסן ROKS-AN is zipper.

Isaac Fried, Boston University

[Isaac Fried]

Closely related is the act רכש RAKA$, 'gain, possess, acquire, procure, accumulate, accrue, amass', as in Gen. 31:18
וַיִּנְהַג אֶת כָּל מִקְנֵהוּ וְאֶת כָּל רְכֻשׁוֹ אֲשֶׁר רָכָשׁ מִקְנֵה קִנְיָנוֹ אֲשֶׁר רָכַשׁ בְּפַדַּן אֲרָם
KJV: "And he carried away all his cattle, and all his goods which he had gotten, the cattle of his getting, which he had gotten in Padanaram"
In רְכֻשׁוֹ = רכ-הוּא-ש-הוּא the internal הוּא U, 'he', refers to the thing itself, while the end הוּא refers to Jacob.

Isaac Fried, Boston University