Wife = Slave?

As my son was "whinning" for Mommy to get him a glass of milk I reminded him how I was not "his slave" and he should ask me nicely. Cassie asked what does Slave mean so I proceeded to explain it to her then back to my laundry I went...A moment later I hear my sweet 6 year old say to her dad...

"Daddy, so does slave also mean a wife?"