better half, my
1. Also, better part. The larger amount or majority of something, as in I won't be long; the better half of this job is complete, or I have spent the better part of my life in this city. Sir Philip Sidney used the first term in Arcadia (1580): "I ... shall think the better half of it already achieved." The variant appears in a well-known proverb, discretion is the better part of valor.
2. Also, my better half. One's (my) spouse, as in I'm not sure if we can go; I'll have to check with my better half. Originally this expression meant "a close friend or lover," and by the 16th century it referred to either a wife or lover. Sidney used it in this way, again in Arcadia: "My dear, my better half (said he), I find I must now leave thee." Today it tends to be used lightly for either husband or wife. "Late 1500s"
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
better half, my
My spouse, usually referring to one’s wife. The term dates from the sixteenth century and originally signified a close friend or lover. Indeed, much earlier the Roman poet Horace called his friend animae dimidium meae, describing an intimacy in which two friends are considered the halves of one whole. The Elizabethans used it for a wife (Sir Philip Sidney in Arcadia, 1590) or lover (Shakespeare, Sonnet 39, ca. 1600). It continued to be used seriously through the eighteenth century and then began to be used more in a jocular or ironic way, as it is today.
See also: better
The Dictionary of Clichés by Christine Ammer Copyright © 2013 by Christine Ammer