NET

21 If a man has marital relations with his brother’s wife, it is indecency. He has exposed his brother’s nakedness; they will be childless.

Darby

21 And if a man take his brother's wife, it is an unclean thing: he hath uncovered his brother's nakedness: they shall be childless.

KJV

21 And if a man shall take his brother's wife, it [is] an unclean thing^K568: he hath uncovered his brother's nakedness; they shall be childless.

KJV Bible Notes

an unclean thing: Heb. a separation.

Strong's

21 And if a man^H376 shall take^H3947 his brother's^H251 wife^H802, it is an unclean thing^H5079: he hath uncovered^H1540 his brother's^H251 nakedness^H6172; they shall be childless^H6185.