An idiom is a collection of words which means more than
the sum of the meanings of each of the phrases' individual words.
Moses leaving Aaron and Chur to deal with the nation
while he received the law
And he said to the elders, Wait here for us,
until we come again to you; and, behold,
Aaron and Hur are with you; if anyone
owns an issue [has a civil claim]
let him come to them.
owns an issue
is an idiom meaning
As can be seen from the underlined words
the Rashi comment is compactly and explicitly combined in the Biblical text.
One can never prove the meaning of an idiom since by definition the
idiom means more than the sum of the meaning of its words.
However there are other verses where the Hebrew Daleth-Beth-Resh, Davar
means legal matter:
And it came to pass on the next day, that Moses sat to judge the people, and the people stood by Moses from the morning to the evening.
And when Moses’ father-in-law saw all that he did to the people, he said, What is this thing that you do to the people? Why do you sit by yourself alone, and all the people stand by you from morning to evening?
And Moses said to his father-in-law, Because the people come to me to inquire of God;
When they have a matter [daleth-beth-resh, legal matter], they come to me; and I judge between one and another, and I make them know the statutes of God, and his laws.