Genesis 4:19

And Lamech took unto him two wives: the name of the one was Adah, and the name of the other Zillah.

And Lamech took unto him two wives,.... He was the first we read of that introduced polygamy, contrary to the first institution of marriage, whereby only one man and one woman were to be joined together, and become one flesh, Genesis 2:24. This evil practice, though it began in the race of wicked Cain, was in later ages followed by some among the people of God, which was connived at because of the hardness of their hearts; otherwise it was not so from the beginning. This was the first instance of it known; Jarchi says it was the way of the generation before the flood to have one wife for procreation of children, and the other for carnal pleasure; the latter drank a cup of sterility, that she might be barren, and was adorned as a bride, and lived deliciously; and the other was used roughly, and mourned like a widow; but by this instance it does not appear, for these both bore children to Lamech.

the name of the one was Adah, and the name of the other Zillah; whose daughters they were cannot be said, no doubt of the race of Cain; the name of the one signifies an "ornament", or beauty, and might seem to answer to the account Jarchi gives of the wife for pleasure, if there were any foundation for it; and the other signifies a "shadow", being continually under the shadow of her husband.