A man might call his wife his better half.
The definition of better half is an expression used to refer to your spouse or significant other.
An example of a better half would be a man's wife.
one's spouse; esp., one's wife: a humorous usage
Origin of better halfUltimately translation of such phrases in Latin poety as animae d&imacron;midium meae, half of my soul (referring to the poet's friend).