Rashi on Exodus 28:28/רש"י על שמות כ״ח:כ״ח

1וירכסו — This is an expression for joining. Similar in meaning is, (Psalms 31:21) “[Thou hidest them] from the רֻכְסַי of men”, i. e. from the union of companies of wicked people. Similar is, (Isaiah 40:4) “And the רכסים shall become a plain” — i. e. the mountains which are close (almost joined) to one another so that it is not possible to descend into the valley between them except with great difficulty, since, in consequence of their closeness to each other, the valley is precipitous and deep — these רכסים, connected mountains, shall become a level plain and easy to travel upon.

2להיות על חשב האפוד THAT IT MAY BE UPON THE GIRDLE OF THE EPHOD — that the breast-plate (not the ring) may be attached to the girdle of the ephod.

3ולא יזח SO THAT [THE BREAST-PLATE] BE NOT LOOSENED — יזח is an expression for “breaking away”. It is an Arabic expression according to the opinion of Dunash ben Labrat.